linux-capture: Add xcb libraries to cmake

Add xcb libraries needed to port the plugin away from xlib to cmake.
linux-capture: Add xcb helper functions for shm

Add new helper functions managing the shm segment with xcb to xhelpers.
linux-capture: Add helper to get xcb screen

Add a helper function to get a xcb screen from a screen id.
linux-capture: Add xcb cursor helper library

Add a new helper library to handle the mouse cursor using xcb.
Since porting the old library without either keeping legacy code or
breaking the api would have been non-trivial, this is added as a
completely separate implementation. Once all code is ported over to
use this library, the old one can be removed.
linux-capture: Add function to check extensions

Add an internal function to check for all the extensions needed by the
xshm capture to work.
linux-capture: Add xcb connection to source data

Add a xcb connection to the source data for the xshm capture for later
use in the porting process.
linux-capture: Add xcb screen to source data

Add xcb screen structure to the source data for later use in the porting
process.
linux-capture: Port xshm handling to xcb

Use the new xcb based xshm functions to attach the shared memory segment
and capture the image from the xserver.
linux-capture: Port cursor handling to xcb

Use the new xcb based cursor library to handle the cursor in the
xshm plugin.
linux-capture: Use xcb to check for extensions

Use the previously added helper function to check for needed extensions.
linux-capture: Remove XLib based shm helpers

Remove the old XLib based shm helper functions from xhelpers.
linux-capture: Port geometry functions to xcb

Replace XLib code with xcb in the geometry helper functions.
linux-capture: Port display connection to xcb

Remove the last bits of Xlib code from the xshm capture plugin and use
xcb exclusively.
linux-capture: Remove unused dependencies

Remove dependencies from cmake that are no longer needed due to the
port to xcb.
linux-capture: Refactor source data

Remove comments from and align members in the source data struct for the
xshm capture plugin.
Merge pull request #312 from fryshorts/xshm-xcb-conversion

linux-capture: Xshm plugin xcb conversion