[vdmkenny]

The inspector edits the selected record as a form, and the outline adds records (#8).

• Forms. Each record's fields and their kinds come from OpenReliant's tables of the language (dte.source.language), through the game's profile: lists of the mission's records or of the game's values (with a find box for long ones), X/Y/Z boxes for a vector, number boxes, checkboxes, and the value's source for the rest. The ship's form follows the Scene design: a Place heading, X/Y/Z, and Angles on one row. A trigger's form sets what it watches, its condition and the values it checks, Repeats and Deferred.
• Edits. Each change rewrites one span of the source, as one step of Undo, in the table's own layout (mission/edit.zig): OpenReliant's syntax tree gives where a value starts, and the editor reads the text for where it ends.
• Adding. The outline's + (Mission · Add a record) adds a ship, a nav point, a waypoint, a flight group, a part, a trigger or a global after the last record of its kind, and selects it. A Problems card's Declare adds one under the name that isn't declared.
• Settings has a back button; the design's three settings pages have it too, with their pictures taken again.
• Queued changes. The interface queues a change while a frame draws, and the app makes it once the frame is drawn, since making it checks the source again and replaces the outline the panels draw from. This also fixes the Problems card's Use fix, which checked the source again while the panel drew its list.

Not in this PR: renaming a record (Declared as), forms of their own for Launch, formation points and a counted trigger's count (their source can be typed), and adding squads, formations and curves.

Docs: docs/editing.md, and Editing records in docs/architecture.md.

Checks: make check (58 tests), and the forms tried in the editor on the guide's first mission.

Closes #8