Remove instance variables from interface
Move “click to open” logic to cell

This will make it easier to change the logic, since 3 different parts of the file browser depend on it: accepting first responder, selecting items, and single-clicking items.
Allow opening files by single-clicking text (rather than icon)

This is enabled via: defaults write com.macromates.TextMate.preview fileBrowserSingleClickToOpen -bool true

Closes #187