[Bf-taskforce25] Hotkeys for mesh selection mode switching.

[joe]

After some discussion with Geoffry and Matt on IRC, it became clear
that for a selection mode-aware system to really work, we need really
fast hotkeys to switch between vert/edge/face selection mode.  The
current hotkey is both extremely awkward, *and* produces a menu, which
makes it very annoying to use (to the point I myself have never really
used it).

We came up with the idea of using q w e for switching modes.  Wkey
would be moved to spacebar, and ekey would be moved to tkey (for
exTrude).  This would help ease the pain as more and more tools are
likely to become selection mode-aware (and thus users will have to
switch modes to accomplish specific tasks).

Changing hotkeys is normally somewhat dangerous, but frankly I believe
it to be necessary, and I certainly intend to do more reorganization
then this.  The (many) hotkey popups we have are in bad need of
organization, and I suspect that many functions may move to different
hotkeys by the time we're done.

Joe