[CSharpBinding] No longer create redundant undo step for inserting a
new line in virtual mode.
Fix needs building check

Mac and iOS projects provide custom checks for NeedsBuilding so the check
has to be done using the project service extension chain.
Declare the add-in identity and dependencies using attributes
Define add-in identity using custom attributes

Defined a Version constant which can be used to declare the version of
an addin. In this way it is not necessary to use a constant value
to declare dependecy versions in all addins.
Add assembly prefix to assembly attributes