FileView: Add quick select file select

[warpdesign]

This PR adds the ability to quickly select a file by typing the first letters:

• typing 'a' will select the first file starting with 'a'
• typing 'abc' will select the first file starting with 'abc' (if there is none, it won't unselect previous file)

I also stumbled upon a bug that I fixed: meta + i to invert the selection worked even if the FileView was not active.