database: Rename start/end to event_start/end, add channel and quality

* Had to rename `end` as `end` is a reserved word in postgres SQL.
`event_end` is more consistent with `video_end` anyway. Updated `start` to match.

* Added ability to specify channel and stream quality in the editor, which may prove useful
if we have issues with a particular stream quality, or if content needs to be captured from
other channels.

DATABASE.md

@@ -125,7 +125,7 @@ Edit input values are initially NULL, but must not be NULL once the state is no
 columns                    | type                               | role        | description
 -------------------------- | ---------------------------------- | :---------: | -----------
 `id`                       | `UUID PRIMARY KEY`                 | sheet input | Generated and attached to rows in the sheet to uniquely identify them even in the face of added, deleted or moved rows.
-`start`, `end`             | `TIMESTAMP`                        | sheet input | Start and end time of the event. Parsed from the sheet into timestamps or NULL. Used to set the editor time span, and displayed on the public sheet. The start time also determines what "day" the event lies on, for video tagging and other purposes.
+`event_start`, `event_end` | `TIMESTAMP`                        | sheet input | Start and end time of the event. Parsed from the sheet into timestamps or NULL. Used to set the editor time span, and displayed on the public sheet. The start time also determines what "day" the event lies on, for video tagging and other purposes.
 `category`                 | `TEXT NOT NULL DEFAULT ''`         | sheet input | The kind of event. By convention selected from a small list of categories, but stored as an arbitrary string because there's little to no benefit to using an enum here, it just makes our job harder when adding a new category. Used to tag videos, and for display on the public sheet.
 `description`              | `TEXT NOT NULL DEFAULT ''`         | sheet input | Event description. Provides the default title and description for editors, and displayed on the public sheet.
 `submitter_winner`         | `TEXT NOT NULL DEFAULT ''`         | sheet input | A column detailing challenge submitter, auction winner, or other "associated person" data. This shouldn't be relied on in any processing but should be displayed on the public sheet.
@@ -138,6 +138,8 @@ columns                    | type                               | role        |
 `video_start`, `video_end` | `TIMESTAMP`                        | edit input  | Start and end time of the video to cut. If already set, used as the default trim times when editing.
 `video_title`              | `TEXT`                             | edit input  | The title of the video. If already set, used as the default title when editing instead of `description`.
 `video_description`        | `TEXT`                             | edit input  | The description field of the video. If already set, used as the default description when editing instead of `description`.
+`video_channel`            | `TEXT`                             | edit input  | The twitch channel to cut the video from. If already set, used as the default channel selection when editing, instead of a pre-configured editor default. While this will almost always be the default value, it's a useful thing to be able to change should the need arise.
+`video_quality`            | `TEXT NOT NULL DEFAULT 'source'    | edit input  | The stream quality to cut the video from. Used as the default quality selection when editing. While this will almost always be the default value, it's a useful thing to be able to change should the need arise.
 `state`                    | `ENUM NOT NULL DEFAULT 'UNEDITED'` | state       | See "The state machine" above.
 `uploader`                 | `TEXT`                             | state       | The name of the cutter node performing the cut and upload. Set when transitioning from `EDITED` to `CLAIMED` and cleared on a retryable error. Left uncleared on non-retryable errors to provide information to the operator. Cleared on a re-edit if set.
 `error`                    | `TEXT`                             | state       | A human-readable error message, set if a non-retryable error occurs. Its presence indicates operator intervention is required. Cleared on a re-edit if set.