added nuget -install and command factory
added command tests,
Merge branch 'dev' of https://github.com/scriptcs/scriptcs into dev

Conflicts:
	src/ScriptCs/Program.cs
added support for local nuget.config
committing missing tests
Merge #130

Conflicts:
	src/ScriptCs/Program.cs
Merge pull request #131 from filipw/dev

nuget -install & package validation