Swapping handles when dragging a handle should be prevented

[amantoux]

When dragging the end handle above the start handle, the selection is lost or behaves unexpectedly.
In case where start (resp. end) handle is moved:

• after (resp. before) the end (resp. start) handle on the same line, the selection should be reduced to the character before (resp. after) the other handle
• after (resp. before) the end (resp. start) handle on some line below (resp. above), the selection should remain unchanged

[amantoux]

@pulyaevskiy can we add this to 1.0

[pulyaevskiy]

Added to the project.