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.
Do not try to invoke target if ribbon control context is null.
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 #55 from draganjovanovic1/ErrorHandlingFix

VstoContribContext ErrorHandlers null bug fix
Merge pull request #51 from jpeterson-isdc/master

Do not try to invoke target if ribbon control context is null.
Merge pull request #49 from Docalytics/master

Outlook plugin without view model for explorer causes error
Merge branch 'ViewLocationStrategyFix' of https://github.com/draganjovanovic1/VSTOContrib into ViewLocationStrategyFix