Start refactoring of IsolateHandler to enable single-threaded mode.
WIP: Continue IsolateHandler refactoring to allow single-threaded execution.
Minor code refactoring (easier debugging).
Rename a few classes to better reflect their meaning.
Comment.
Remove "Isolate" term form abstractions.
Minor code cleanup.
Address code review feedback, and minor code cleanup.
Merge pull request #3352 from rpaquay/alternate-isolate-handler-implementation

Allow services to run in application isolate.