Blender Git Loki

Keymap: Remove pie menu from tab-key

Based on discussion with @eyecandy & @venomgfx,
we agreed that Tab drag/click, is too easy to accidentally press
while moving the cursor.
It's also not typical to activate the operator on release which
introduces a small lag switching edit-mode.

This is a shame since in some ways its a nice way to re-use the key,
overall it just feels a little too unpredictable for such an important
action.

This commit makes the following changes.

- Tab: toggles edit-mode.
- Ctrl-Tab: opens pie menu.
- Ctrl-AccentGrave: toggles manipulator.

Note, while AccentGrave isn't always available
this shortcut is not essential.