Swap adjacent items with J/K

The change adds a new `swap` method to `todo.Todos` and binds that to J and K
respectively.
Got the background color of focused list items working correctly
modified highlight method to highlight using urwid text markup

see: http://urwid.org/manual/displayattributes.html#text-markup
got editing of todos working nicely
add some edit keybindings
Merge pull request #11 from matze/add-swap-reordering

Swap adjacent items with J/K
Merge branch 'master' into urwid
update todo highlight test
added swapping todo support with J, K in the urwid ui
don't import ipdb
fix completing todos
added a footer, refactored urwid_ui a bit
create move_selection methods
move colorscheme to its own file
simplified moving the selection, can now add todos
implement deleting todos
added a pending and done count to the header
can't reliably set the cursor position in an edit box, so don't prepend the creation date to new todos for now
implemented saving and reloading the current todo file
first stab at filtering multiple contexts and projects