20160912 BER: Better code: states.py: classes EditEntryState and 
  AdjustEntryState have same methods exit() and set_focus(), maybe join them?

20151130 BER: templates/zeiterfassung2: Really sort by date, right now the 
  sorting it sometimes skewed if the week wraps around the end of the month.

Older:

- Create a 'Help-Widget' to give the user an information about all possible
  keys.

- reimplement RPN input for current getan implementation (28489e672e61)

- The sum of previous times and currently running time should be displayed as
  in previous versions of getan.

- The currently running time should be shown near the project.