Fixed issue with Outlook plugins that don't have a view model for the explorer

Outlook plugins that didn't have a view model mapped to an explorer
would call a null reference exception. Moved up null check to earlier
for view models so that this wouldn't happen.
Implemented ribbon xml rewrite for dynamicMenus so that callbacks work; closes #52
Added logging to RibbonFactoryController's invoke method so that logs would should when calls other than gets would show.
Merge pull request #49 from Docalytics/master

Outlook plugin without view model for explorer causes error