Add "app printer activity" and always keep the print service state

updated. Also fiddle with the UI to use more standard values.

To be sure the print service state alwasy updated I changed
PrintManager.getPrintServices to return a loader which just wraps a
registerListener/getList/removeListener combo.

I also added a new function to enabled/disable a print service to be
keep all updating logic inside the PrintManagerService->UserState.

Then I changed all code to use this new interface.

Detailed comments:

PrintServiceInfo:
- I had to add the enabled state to the PrintServiceInfo as some users
  of PrintManager.getPrintServices want all services but then display
  different data depending on the enabled state. Of course I could have
  created two PrintManager.getPrintServices-loaders to load the two
  separate list of services. I think it is much easier to add this
  property though. It is updated every time new data is returned to the
  PrintManager.getPrintServices-loader.

AddPrinterActivity:
- This is shown as a dialog-style overlay to indicate that the user will
  return to the select-printers activity. It contains of three list that
  are updated via separate loaders.
- The recommended services will be added later to keep this path set
  small.

PrintActivity:
- There are two small places where we have to update the data when we
  get a new list of print services.
  - In very, very rare conditions it can happen that the print service
    of the current printer gains or looses the "advancedOptions"
    activity
  - If we have no enabled print services we want to show "Add printer"
    instead of "All printers...".
- Also the print registry is not the only loader anymore, hence we have
  to assign loader ids to it to not conflict with the other loaders in
  this activity.
- Small bug in onPrintersChanged: If a printer is selected and the print
  service of this printer gets disabled the holder goes into "removed"
  state which disables the printer. When the print service is then
  enabled again, we forgot to re-enable the holder.

PrinterRegistry:
- The registry assumed that the FusedPrinterProvider was the only loader
  in the activity. This is not true anymore, hence it has to assign the
  appropriate loader ids.
- The FusedPrinterProvider has an internal loader, hence we have to
  forward a loader Id into it.
- The PrintRegistry is only called backed for a single loader, hence no
  need to check the loader-id.

SelectPrinterActivity:
- The AddPrinterDialog was removed as we now have the
  AddPrinterActivity.
- Added a loader for the enabled services to update the empty state.
- Added dedicated loader Id for the PrinterRegistry again.
- If we have no enabled services, the SelectPrinterActivity chainloads
  the AddPrinterActivity as this is the only thing the user can do
  anyway. "Save a click". This should only happen when the activity is
  create the first time.
- Moved the "add printer" from the menu item to the list of printers as
  suggested by UX and Zach.

PrintManagerService, UserState and IPrintManagerParamtersTest:
- As the only place where the print service state is updated is now the
  userstate, we have no more sychronization problems. Whohoo.
- The users can now register for changes to the print services similar
  as they can register for changes to the print jobs.
- UserState.getPrintServices is the only function can exposes any
  knowledge of the print services to the outside world.

Change-Id: I9be2c7300431e06aaff9bdf7eb36120d869b56ac