Behavior should not trigger when the tracked value has not changed.

Behaviors are specifically for animating changes in value. When the
value has not changed, do not trigger the animation. This ensures
the animation system is not unnecessarily woken.

[ChangeLog][QtQuick][Behavior] Do not trigger a Behavior when the
tracked value has not changed.

Task-number: QTBUG-21549
Change-Id: I5b20121ccfb75ea5ebf86705df89891c94cf6e7e
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>
Reviewed-by: Alan Alpert (Personal) <416365416c@gmail.com>
Fix SpringAnimation in Behavior when current value is set.

Fixes regression introduced by d489f2f6549a86b3949004d1c8ec68487fc2adb7.
We now only avoid running the animation if the Behavior wasn't already
mid-animation. This ensure correct behavior for SpringAnimation, and
also correct state for 'running'.

Task-number: QTBUG-21549
Change-Id: I0f97813294cca22fb7a273e222fa0549c6de9ca7
Reviewed-by: Alan Alpert (Personal) <416365416c@gmail.com>
Merge pull request #15 from mbrasser-jolla/behavior-fixes

[qtdeclarative] Behavior fixes