Fix wrong placement of i3bar when connecting/disconnecting outputs

Fix wrong placement of i3bar when connecting/disconnecting outputs

When connecting or disconnecting an output, i3bar reconfigures its
windows. This also included an unmapping of the bars, and a remapping of
all docked bars. Thus, the bars were misplaced when a monitor was
disconnected.

This commit assures that the remapping of the bars only takes place,
when the mode has actually changed. This patch also takes care of an
inconsistency when pressing the bar_modifier while switching the mode.
Also, the xkbDisplay is now closed correctly, when deregestering the xkb
keyevents.