Add "sort by title" capability

This patch implements 'sort by title' for file list.

Deft's powerful filtering feature helps users to narrow down to
manageable number of files from your pile.  If you have many common
prefix in your title, sort by title gives you much cleaner view of the
list, grouped by title.

It also helps users with too many files.  With huge number of files,
list might not fit in the window with a simple filter. You might be
missing your old files.