Bug 479049

Though I've generally had a positive experience by switching from VSCode & document editors to Ghostwriter, the absence of some gestures is inconvenient. Notably, what I would be happy to see:

- up arrow key could function like the Home button when the cursor is at the first line of a file.
- down arrow key could function like the End button when the cursor is at the last line of a file.
- `ctrl+[` & `ctrl+]` for indenting selected line(s). This differs from using tab to indent the current line, as when nothing is selected, a tab inserts spaces/tabs at the current cursor position; `ctrl+[` would instead indent from the beginning of the line. 
  - Though you can technically get Tab to work this way mid-line via shift-select shenanigans, it is a needlessly hackier solution.