Add a command palette

[lhecker]

We already got a fuzzy matcher (src/fuzzy.rs), now all we need is the matching command palette! We can then use it for representing the existing encoding picker, indentation picker, and file picker dialogs.

My biggest open question is: What shortcut do we use? If you take the union of all keyboard keys that popular terminals don't use for themselves already, you're practically left with only A-Z. 😢 Perhaps Ctrl+P is still our best bet, even if it doesn't work in VS Code.

As part of this we should solve #228.

[juemrami]

ctrl + shift + p is my suggestion. Thats also VSCode's default keybind for the command palette

[ryanmda]

However, that opens the Windows Terminal palette by default 🙂

[expikr]

Ctrl+L is burned into my muscle memory for doing everything in the browser. Or for some that would be Ctrl+K, which also matches VSCode.