Blender Git Loki

Bind Camera to Markers - Various tweaks to make this nicer to work with

Based on discussions here in the office, this commit introduces a number of
changes to make the "Bind Camera to Markers" feature (introduced during Sintel
to facilitate camera switching, and now an integral part of the UI for doing this)
nicer to use.

Main changes:
* "Camera Markers" are now drawn using Camera icons, making it easier to
distinguish between them and other ("normal") markers

* "Camera Markers" will display the name of the bound marker, making it
easier to see what camera each marker uses. This will then also stay
in sync with the camera being used (though a manual refresh is needed
after renaming objects to make the timeline update), fixing the problem
where the marker's camera and the name get out of sync.

* Behaviour of Ctrl-B has been modified to make it easier to quickly add
these markers. Now, it will directly add a new marker on the current frame,
bound to the currently selected camera object. If there's an existing marker
on that frame, the existing marker's camera will be replaced instead of making
a new marker.