Fixed a number of issues, all revolving around VCell locking up under the right (wrong) conditions

[CodeByDrescher]

The core issue behind this PR: #1331

Fixes introduced in addressing this issue:

1. VCell now sports new extensions to the ClientTaskDispatcher class: a) ClientTaskDispatcher::dispatchAndWait will now indefinitely block a dispatched list of tasks, until they are completed. b) ClientTaskDispatcher::dispatchWithFuture returns a Future<Hashtable<String, Object>> object, which can be used to check if the results are done, or impose a manual timeout on the operation; the underlying mechanism behind ClientTaskDispatcher::dispatchAndWait
2. VCell no longer freezes up when disconnected and not trying to save a model in a closing window.
3. VCell now gives error messages when attempting to save a model while disconnected, informing the user it can't seem to contact the database, and if they proceed a DataAccessException. They are no longer stuck behind a progress dialog that goes on for too long. The window will not close until either No is re-selected, or the client is reconnected.
4. VCell now realizes much, MUCH sooner it has been disconnected (up to 5 seconds).

[CodeByDrescher]

Closes #1331