Move RevitTestFramework to .NET Framework 4.7

[tshcha]

Purpose

Since Revit has been moved to .NET Framework 4.7 it is necessary to move all projects which uses RevitAPI.DLL, RevitAPIUI.DLL etc. to .NET Framework too...

Declarations

Check these if you believe they are true

• [X] The code base is in a better state after this PR
• [X] Is documented according to the standards
• [ ] The level of testing this PR includes is appropriate
• [ ] User facing strings, if any, are extracted into *.resx files
• [ ] All tests pass using the self-service CI.
• [ ] Snapshot of UI changes, if any.

Reviewers

Phil Xia

Aaron Tang

FYIs

[mjkkirschner]

@tshcha sorry missed your PR! I just merged the same change.