Use the Palaso library browser adapter

* Remove any direct gecko dependency from Chorus
* Remove the BetterBrowser in favor of using the XWebBrowser
  from the PalasoWindowsForms library
Complete the removal of specific gecko dependency from Chorus

* Use the new IWebBrowser interface from Palaso to hide all
  the Gecko specific code
Clean out obsolete code to address review comments

* Follow up to remove direct gecko dependency work
Merge branch 'master' into RemoveDirectGeckoDependency

Conflicts:
	src/Chorus/UI/Settings/SendReceiveSettings.Designer.cs
Merge branch 'RemoveDirectGeckoDependency'