Code Cleanup: Disable unnecessary prints when doing file IO
Tweaks to gutter formatting

* Slightly wider (better for long files)
* Softer color for line numbers
* Nicer bookmark appearance
Set lexer according to extension and also line wrapping defaults (per type)

The lexer <-> extensions stuff is hardcoded and defined inline so far.
Some refactoring will be needed to split this out eventually, but for now
it works quite well for what it is.