fix keybindings

- `esc` only closes modal if modal is visible (fix #548)
- `ctrl+b` now saves a bookmark of current map view
- `ctrl+/` is now help (fix #715)
- `ctrl+alt+s` is now export (fix #662)
- ~~`ctrl+[1-9]` is now tab switch. The old `ctrl+alt+[1-9]` was super awkward, and when running studio as an app, rather than in browser, doesn't conflict with anything.~~