Added a Scala preference for Mark Occurrences

Added a toolbar button for quick access.
Fixes #1001466
Fixes problems in preference state sharing

Using only Boolean, and correctly starting the toggle handler listener.
Initialize symbols for primitive types on compiler startup.

The nightly build uncovered a race condition in the indexer, that stepped on
a case where `definitions.ShortClass` was not yet loaded, triggering the
symbol loader.

Needs back port. Should fix flaky presentation compiler tests.
Disabled flaky debugger ``RemoteConnectorTest`` tests class

Re #1001464
Merge pull request #311 from dotta/issue/disable-debugger-remote-tests-1001464

Disabled flaky debugger ``RemoteConnectorTest`` tests class
Merge pull request #299 from skyluc/issue/mark-occurrence-preference-1001466

Added a Scala preference for Mark Occurrences
Merge pull request #310 from dragos/issue/indexer-race-condition

Initialize symbols for primitive types on compiler startup.