xfwm: support for 2d pagers

[Paramjit Oberoi]

> Ok applied. All shortcuts are set to "none" by default for now though.

Regarding shortcuts:

The current default shortcuts for workspace-related actions are:

    next workspace              Control+Alt+Right
    prev workspace              Control+Alt+Left

    window to next workspace    Control+Alt+End
    window to prev workspace    Control+Alt+Home

I recommend the following defaults:

    next workspace              Control+Alt+PgDn
    prev workspace              Control+Alt+PgUp
    up workspace                Control+Alt+Up
    down workspace              Control+Alt+Down
    left workspace              Control+Alt+Left
    right workspace             Control+Alt+Right

    window to next workspace    Control+Shift+PgDn
    window to prev workspace    Control+Shift+PgUp
    window to up workspace      Control+Shift+Up
    window to down workspace    Control+Shift+Down
    window to left workspace    Control+Shift+Left
    window to right workspace   Control+Shift+Right

* Why change existing defaults for next/prev workspace?

  The arrow keys just make more sense for up/down/left/right navigation.
  Moreover, with the 1-row XFCE pager, prev/next is equivalent to
  left/right, so your learned reflexes will still do the same thing.
  Also, PgUp/PgDn express the semantics of prev/next workspace better.

* Why change the defaults for move window to next/prev workspace?

  It's better for the change-workspace and move-window-to-workspace keys
  to be in sync.  Also, atleast one email suggested that these keys are
  not frequently used, so bringing them in sync might make them useful.
  I know I use these keys on a fairly regular basis, and I wouldn't if
  they weren't similar to the change-workspace keys.

* What about the workspace_n_key & move_window_workspace_n_key shortcuts?

  That's a problem.  The current binding for these keys is:

    workspace_n_key              Control+Fn
    move_window_workspace_n_key  Control+Alt+KP_n

  This isn't consistent with the Control+Alt to change workspaces,
  Control+Shift to move windows pattern.  However, changing these
  defaults will be counter-productive, I think, and they should be
  left as they are.

-param