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
• 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.