Reorganize package folder

[CharliePoole]

Now that we are using a monorepo, the package folder needs to be changed to avoid unwanted dependencies among the packages we are testing.

CURRENT STRUCTURE

package
   tests
      choco
         folders for installed gui and extensions used
      nuget
         folders for installed gui, engine and extensions used by each (PROBLEM)
   results
      choco
         testcentric-gui
           folders for individual package tests
      nuget
         TestCentric.GuiRunner
            folders for individual package tests
         TestCentric.Engine
            folders for individual package tests

PROPOSED STRUCTURE

packages
   tests
      TestCentric.GuiRunner
         folders for installed gui and extensions used
         results
            folders for individual package tests
      testcentric-gui
         folders for installed gui and extensions used
         results
            folders for individual package tests
      TestCentric.Engine
         folders for installed gui and extensions used
         results
            folders for individual package tests

NOTES

1. Pluralizing packages seems to make more sense
2. Since nuget and chocolatey packages have different naming conventions a separate folder for each doesn't seem to make sense any longer unless we think it's needed for ease of use.
3. Placing results under individual test groups is something I've been wanting to do for a while.
4. It appears that the Engine package tests are currently loading extensions under package\tests, which is an error.

This is only a build change but it would be easy to break things, so I'll most likely want to do it in multiple steps.

@rowo360 What do you think?