Fixed/unified all xml.in headers.

(LP: #1066823)

Problem: Editors like gedit and others will not recognize *.xml.in files as xml, so if opened there is no syntax highlighting making those files harder to read.
This commit fixes this by adding <?xml version="1.0" encoding="UTF-8"?> to all *.xml.in files in lp:compiz. Fixes: https://bugs.launchpad.net/bugs/1066823. Approved by Daniel van Vugt.