Devoncarew minimap tweaks

Tweak the minimap:

- move the minimap inside the editor (to the left of the scrollbar)
- make the minimap icons slightly bigger, to make it easier to hit with a mouse

Also:

- fixes an issue where we couldn't edit as text file that started with periods
- added some new file types that we can open by default (like .gitignore)

@umop for review