Revamped viewer cache preference controls.

Implemented improved cache control user interface, changes approved by wolf.
* Moved viewer cache controls from the setup preference panel to advanced
* Changed cache size control slider into a spinner
* Readded a clear cache button along with a cache clear confirmation dialog
* Renamed the reset button to "Default Location" to clarify its function

Related JIRAs:
ER-815
ER-816
ER-818
ER-820
ER-821
ER-831