Disable CSS custom filters

CSS custom filters aka CSS shaders have been removed from Chrome and
Safari. We should follow the same steps and disable the feature in
our builds.

Change-Id: Iac63a48c1853683d764ee0401b45d15530c37e2b
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>
Make building QtTestBrowser simpler

The QtTestBrowser needs qttestsupport and qttestsupport needs fontconfig
on linux, unfortunately fontconfig is only enabled on webkit developer
builds. This patch add fontconfig when qttestsupport is enabled. This
makes it possible to build the QtTestBrowser in a production_build
by only overriding build_testbrowser and build_qttestsupport.

Change-Id: I7d49368bee82bb1eb7bc9b5d4eeaf714a3d737f8
Reviewed-by: Michael Bruning <michael.bruning@digia.com>