Settings for which keystrokes two-finger swipes generate

## Summary
* At present `two-finger-swipe right` generates a tab and `two-finger-swipe left` sends an escape character to the terminal.
* It would be nice if this were customizable ... but I don't know how to add settings to `a-Shell` (via either `config` or `System Settings > a-Shell`).
* E.g. making `two-finger-swipe-right` send `Ctrl+]` for more efficient `vim` help browsing.

Tabs and escapes are generated here:

https://github.com/holzschu/a-shell/blob/0868ecd23bda2a82aceda34aea193ada3bfced2b/gestures.js#L394-L399

Thank you for your help with implementing touch gestures!