Move xcb include/link directives from jami to libclient.

Relates to <#882>.

This problem was discovered when attempting to build the test suite:

   ld: ../src/libclient/liblibjamiclient.a(avmodel.cpp.o): undefined
   reference to symbol 'xcb_get_setup'

* CMakeLists.txt: [!(APPLE or MSVC] Move xcb includes and link directives to...
* src/libclient/CMakeLists.txt [!(APPLE or MSVC]: ... here.

Change-Id: If9b6653e157081300caad8f13cafe4979a49630b