Unittest the TUI using pyte

pyte is a simple Python-based terminal emulator. This allows screen-scraping an application running in a different pseudo-terminal which is the main idea behind the unittests for the curses TUI.

Closes #16 (closed)

Unittests for the following functionality should be added:

• normal list view
• getting the current label This is actually rather difficult to test on its own. A failure should show up nicely in the other unittests' traceback, though.
• user color configuration
• user key binding
• resize handling (optional for this PR to be merged)
• the following commands and their resulting effects:
  • add
  • edit
  • delete
  • export
  • filter
  • help
  • open
  • quit
  • show
  • sort
  • wrap
  • jumping to top, bottom, home and end
  • scrolling up, down, left and right