Add creategroup and destroygroup dispatchers

[ChrisHixon]

The only way I see to create/destroy a group is togglegroup. I'd like to bind destroygroup to a different key to help prevent accidental ungrouping. It its current form, the ungroup (destroyGroup function) can spawn and split windows in a somewhat unpredictable way, (especially if unplanned) and it can be a big mess to clean up.

To expand upon this, destroygroup could have some options. One option: ifempty: destroy the group only if it's empty (well, one window) - the group would be locked for ungrouping until only one grouped window remains. With that option, the user could chose to ungroup the windows how they like, and finally close the group. Another thought: add an option to prevent a locked group from ungrouping (actually, is that current behavior?) Other options could add more control of ungrouping... what are some more controlled ways to ungroup? I think I'd like the windows to ungroup into equal splits horizontally or vertically that exactly take place of the grouped window - no surprise reshuffling of the workspace. Current concepts could determine horiz/vert (mouse position, split direction, etc.)

I plan to work on ideas for myself as a plugin, and perhaps eventually submit a PR. In the meantime, what do others think about the topic of ungrouping?