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
RibbonFactory IViewLocationStrategy bug fix (default loaded only once, changing it has no effect)

- IViewLocationStrategy injected through constructor of RibbonFactory to VstoContribContext (fall back to DefaultViewLocationStrategy if null)
- changed IRibbonFactory LocateViewStrategy property to getter only as value of property is used on RibbonFactory construction time only
- added constructor overload for all classes inherited from RibbonFactory
Merge branch 'ViewLocationStrategyFix' of https://github.com/draganjovanovic1/VSTOContrib into ViewLocationStrategyFix