Move Tab to separate file

Also add an new function Tab.getTabLabel.
Fix JSLINT warnings
Fix bug where mode was always 'text'
Remove unused loading animation
Initial version of file explorer

Currently it acts as a tab.
Fix bug with keyboard handlers

The keyboard control was not handed over correctly
when closing the command line.
Make tab switch keybindings work in explorer view
Deliver the project files as a hash

… instead of a flat list. This data structure
is easier to work with for the file explorer.
Make it possible to navigate right/left #explorer
Cleanup
scrollIntoViewIfNeeded #explorer
Update ace