relocate the "framework-only" to stripes-testing repo

A new repo, stripes-testing replaces the framework-only branch of ui-testing. This new repo, based on ui-testing, will contain just the parts needed to invoke tests, but no UI module dependencies or UI tests themselves. Those tests will live within the respective apps and platforms containing the code that is exercised.

This new stripes-testing repo also becomes the logical home for all Stripes related testing documentation.

STCLI-92 will update the CLI to use stripes-testing. After CI has fully moved to platform-core-based testing, ui-testing can be deprecated.