CPS Custom In Memory Profile option

[mitchcapper]

Mostly the same as #147
Some additional logic added to avoid creating the profile / setting it active unless a true user action or on startup project changed when we have at least one command arg in the CLI window (doesn't care if that arg is enabled or not).

Note option added to option page in style of new format from #150, if merged before #150 will not look correct.

Removed the enable/disable plugin option will wait to hear on comments in #147 and then will do a separate PR.

[Irame]

Was there a issue that let you to implement TreeContentChangeUserEventIgnore?
The only thing I can think of is, that the TreeContentChanged event gets triggered to often. But TreeContentUserChanged is only used for CPSCreateAndSetProfileIfUsed and this method has a debounce already.

[mitchcapper]

With your other change may not be needed. My goal was not to set us active or create our profile unless the user already has items in the cli or makes changes to the cli. Creating a user interaction occurred event was my way to do so.

[Irame]

I rebased the pull request into its own branch dev/cps_inmemory_profile.

• I added a minimum version of Visual Studio 17.5 to your first commit (now 789c66c) because I had issues with 17.4 and Microsoft.VisualStudio.ProjectSystem.Managed v17.5.3-gbf0428edc0.
• In your second commit (now 84937f9) I removed the TreeContentUserChanged event and used the new TreeContentChangedThrottled.

I don't know how to rebase with changes on GitHub so I will just close this PR and you can open a new one I you want to add anything.
Thanks for the contribution, it's greatly appreciated!