Rewrite "Open with" executable finding mechanism.

* Set the executable path up in OpenWithManagerDialog,
  rather than when opening files.
* Add logging for errors starting the detached process.
* Add names to JobActionFactories.
* Add filesystem autocompletion and check permissions of
  executable.
* Add "Apply" button and keep track of dirty state.
* Validate executables when closing the manager dialog and
  prompt to change bad executables.
* Change valid text color from green to black.
* Clean up documentation.

Change-Id: I7500325b389ada283b993048050f30713ea30fed
Merge topic 'open-with-fixes' into master

37e424e2 Rewrite "Open with" executable finding mechanism.