Add ability to hide completed dailies.

While I was at it, I also did a bit of refactoring in general around the hiding
of completed todos/dailies.
renamed Daily tabs to save space, removed To-Dos from new code because compled/all tabs were blank, decoupled To-Do code from Dailes code to allow future changes (e.g., "Dated" tab for To-Dos)
move Dailies "All" tab to the first position, to make it the default (I hope)
make All the default tab for Dailies (instead of Due)
Merge pull request #4129 from Alys/Gaelan-hide_completed_dailies

Add ability to hide completed dailies (Gaelan's changes with fixes for merge conflicts etc)