Move view class to view directory.

Move lib/atom-svn-view.coffee to lib/views/file-list.coffee.
Add a couple of keybindings.  They don't work.
Make next/previous work.

Remove useless model lib/models/file-list.coffee.

From the main view, maintain an array of views per file.  When moving to the
next/previous file, update the `current` pointer and also call `deselect` or
`select` on the file views, as appropriate.  Each file view maintains whether it
is the currently selected one.