1. Address the null reference exception when a project dependency is
broken.
2. Address the duplicate key issues after the logic of redirecting
System pacage to reference assembly was added
Update projectmodel-server and tests
1. Fix test timeout caused by undisconnected socket;
2. Update project model server
Rather than keep a map that will have to be constantly updated every time
a new argument gets added to a compiler, the 'additionalArguments' option
will allow users to directly add arguments to the underlying compiler.
