Ported the following tools
* borderselect
* invert selection
Note: while porting these, I noticed a few issues with some stuff that still needs to be cleaned up.
Events handling in scrollers won't work yet, for the useful select all in frame(-range) or select all in channel(s). We should probably review ways to expose this more clearly in the UI too.
* Brought back backend for editing keyframes IPO/IPO-Curves. Did some refactoring work here that will still have to be verified when operators using them are added.
* Animation channel filtering code now returns the number of channels filtered (for Action Editor to set totrect of channels - TODO still!)
* View2D - made function to check if mouse is in View2D scrollers an API function
* Renamed keyframe related files. The old names were too clumsy.
* Started porting click-select operators for Action Editor. These don't work currently, as the events are being stolen by the markers. This needs to be fixed ASAP.
