Fix when remove is grayed out

[erictwalker18]

Right now, you can only remove files that have been staged...

Remove should allow you to remove any file that is in the index at any time, but should perhaps pop up a warning. This can probably be delayed to the index remake

[calebbraun]

This is another reason (in addition to checking out unstaged files) I think we should consider showing all of the files in the index. The 'remove' and 'checkout files' buttons are both affecting files in the index that may or may not be staged.

We still need to determine where the 'remove' button should go (issue #397 ), but it may make sense to move it to reflect that it is removing files from the index first and foremost, but does not need to remove them from the working tree (using the --cached option).