Several bug fixes (#211, #209 and more)

* Add /\ (slashes) to escaped characters in column name.
* Fix: if column name has only type (like "::x") the table was broken.
* Fix: update to latest pivot table (fixes #211 and adds features).
* Make sure table or pivot table don't overflow.
* Fix: user can't create another dashboard after creating one (#209).
* When changing data source, save query only if it was changed.
* Include data source id in job "lock" (otherwise same query won't execute at the same time on different sources).
* Add favicon.