make the DefaultActivity components rearrangeable

[durka]

I'm not sure if this is a good idea, but I think it is, because it can simplify the preferences a lot while adding more configurability. But it can wait until after the next release, I think. I just wanted to write it down.

Here is my n-point plan to reorganize the UI preferences:

1. kill all of the "show/hide X" checkboxes
2. kill the current DA layout hierarchy and put everything in a flat AbsoluteLayout (or similar)
3. make a new configuration mode which shows the same content as the DA, as well as a "palette" below with all of the available widgets (clock, torch button, camera button, battery indicator, custom widget, ...)
   • (the palette will obviously change if some of the buttons are moved into hV's radial menu)
   • You can drag things back and forth between the palette and the DA, and also freely rearrange them within the DA. Things left in the palette will of course not be displayed at all when the DA comes up.
   • Maybe if you tap on one of the things, a toast or dialog pops up explaining what it is?
4. ???
5. Profit! Open source!