Port wmscapabilities-example to ExtJS 5.0.0

The workaround in the src/GeoExt/data/reader/WmsCapabilities don't seems
to be best practice but it's allready used in src/GeoExt/data/reader/Attribute.js
(3e79ffee14a4f7467244bd6d387e0fa301cd5a0) and just works fine.