Now it is possible to 'protect' action channels and constraint channels.
* When a channel is 'protected', the only operation possible on keyframes
is selection. All other operations are not able to be performed.
* The padlock to the right of each channel's name toggles the protection
status of that channel. You can only alter the protection status of one
channel at a time.
Todos:
* Menus still pop up when trying to do stuff to keyframes even if
all the keyframes selected are from protected channels.
* Shapekey channels shown in action editor should also get locks
6c138fc6a9