bbkeys

The attached patch implements sendToNextWorkspace and
sendToPrevWorkspace. You can use it from the config
file like this:

[sendToNextWorkspace] (Mod1-Right) {true}
[sendToPrevWorkspace] (Mod1-Left) {true}

The parameter is string and if set to "true" or "1"
will also cause the workspace to follow the window
(similar to what middle-click on "send to workspace"
does in Blackbox).

Otherwise, the window is simply sent to the next/prev
workspace.

This patch has one shortcoming: I couldn't figure out
how to also make the window focused when setting the
above to true. window->raise() appears to work as
expected so I've included it, but window->focus()
produces weird results.