+ Add Communication Transport MEF classes
+ Add initial SMTP transport class
+ Create system defined type for communication channels
+ Initial Email control
+ Update communication channel to use MEF rather than defined type
Add Component FieldType and FieldAttribute for selecting MEF component attribute values.
Exclude migration in prep for development branch merge
Merge remote-tracking branch 'refs/remotes/origin/develop' into feature-dt-communication

Conflicts:
	Rock/Rock.csproj
Recreate communcation migration after merging in develop branch
Update Communication page to save/send communications
More communicaiton changes
Convert controls used by communication channels from UserControls to ServerControls
+ Update communication page to maintain state using ViewState rather than saving/reading to DB.
+ Refactor how mergefields are organized
Fixed rendering of attachment delete icon
Add recipient ShowAll and RemoveAll buttons
Update recipient list to include status css class, and only allow removing of pending recipients
Fix the AdditionalActions functionality so that you can edit security for a block's additional attributes (i.e. Approve)
change recipient class to be lower-case
update delete confirm message to reflect only removing Pending recipients
Add communication/recipient status, add validation, fix disabling of recipient delete option
Check Scanner - Bug fixes and tweaks
Check Scanner - Bug fixes, sweeps, and tweaks