Fix overwriting of custom shortcuts, escape in text mode (some systems only) cherry picks

Cherry-pick of !3232 (merged) and !3258 (merged)

What each commit does:

1. Some user shortcuts get overwritten when adding other ones (bad! don't want this in 1.1.x)
2. Escape doesn't work with the text tool (should go back to Select tool) for some users. (fix is small/safe)
3. Some system shortcuts get written into the shortcut file while you're adding a custom shortcut. This prevents that. Previously we didn't have enough information to know the difference, and before that (e.g. in 0.92.x) we explicitly added specific shortcuts when needed, rather than writing out the entire user shortcut file. (biggest change, but this logic is fairly contained)