Merge pull request #1645 from SignalR/null-check-hub

Added a null check for the Send and Group methods in Hub and Persistent Connection
Added install.sql file
SQL message installer now uses install.sql file
- Removed unneeded "SignalR_" prefix from table names
- #1631
Updated ScaleoutMessageBus to enable queuing of messages.
- When the backplane goes down it can indicate a disconnect to the
  base class so that it queue any new sends. It can also indicate when
  the connection is back alive so that the queue can be released.
Limited the task queue when the connection is down.
- Extended task queue functionality to enable a hard limit.
- Return failed task when the queue is full.
Fixed fxcop issue.
SQL message bus install script fixes
- Handle concurrency of multiple servers attempting to install DB simultaneously
- Fixed bad variable reference
- #1633
Queue calls to OnReceived in ScaleoutMessageBus.
Rename variable.
Fixed fxcop error
End after the second ping in longPolling custom query string test

- Previously the longPolling transport would ping after its test was complete
  causing subsequent runs of the same test for other transports to fail.
Make HubGroupFacts.js pass with simultaneous runs.

- By making the group name "random", it is a lot less likely that multiple
  browsers running the tests in HubGroupFacts.js simultaneously will cause
  issues.
Calling DemoHub.DoSomethingAndCallError while AjaxSendFacts.js

is being run no longer causes tests to fail.
Handle connection.start.fail in test.utilities.js

- output reason for failure
Added checks for null and empty values in the Send and Group methods in Hub and Persistent Connection

#1265