Keep selection of tests on Project Tree.

[HelioGuilherme66]

This was already identified, but now have other situation. https://github.com/robotframework/RIDE/projects/1#card-44988576

If user has test in a paused state and changes >code from outside all current ride states got >reseted, even if not paused for example i runned some suite and i have failed and passed tests all tests are checked inside suite if i change file from outside of a ride all test checkboxes and statuses will be >dropped

• [ ] When file is modified from external editor or Git commit
• [x] ~~Also happens when Saving from Text Editor~~
• [ ] We must save and restore Tree selection on these cases.

[HelioGuilherme66]

This is too complex to fix in 2.1.