TestDrive scoping

The test drive is created in describe and when moving to Context its "state" is saved. When moving from the context files created in context are deleted. This is done purely on full path basis so changes made in context to Describe-scope files are kept. All test drive related functions moved to TestDrive. All tests regarding the test drive  moved to TestDrive.ps1. 
Adding exception for TestDrive to the Global scope polluting test was needed. The test is not working properly anyway. :( Some variables like MockHistory are present in the scope after Invoke-Pester is finished.