Behaviorally: This change makes it so that Enter will never cancel
a dialog, unless that dialog only contains info to be read. Escape
will never unpredictably be treated as Enter. And some dialogs without
Escape to cancel, now can be canceled with Escape.
A lot of this just refactors dialogs to define the cancel button
at the top, not as a hotkey on a cancel button deep in the XML.
I think this makes enter/escape behavior in dialogxml files more
legible at a glance.
- On load, the game now detects graphic sheets and sounds whose IDs are "discontinuous", as well as graphics intended to directly replace preset graphic sheets.
- Edit sheets dialog can now handle "discontinuous" graphics. (The edit sounds dialog already could.)
- Edit sheets dialog prompts user to create a new sheet if there are none already, and also if there are some but not ID 0 (in the latter case they can cancel and still edit the sheets).
- Edit sheets dialog prompts user to convert sheets if the scenario is legacy, rather than doing it silently
- Edit sheets dialog now has "new" and "delete" buttons
- Edit sounds dialog now has functioning "delete" button
