don't build server plugins if server isn't built
[processing] fixed handling of parent algorihtms in modeler

Fixes #11750
[proccesing] added compiled ui files

This will make it easier to test new versions of processing for some users
don't build server plugins if server isn't built
* fix server plugin build on windows
* move src/mapserver to src/server (IMHO better name and in sync with
  python/server)
* rename cmake option WITH_MAPSERVER to WITH_SERVER
* rename define MAPSERVER_HAVE_PYTHON_PLUGINS to HAVE_SERVER_PYTHON_PLUGINS
debian packaging update for python server plugins
[composer] Make html tests text-free

Minimises cross platform rendering differences
Add some test images and tweak test tolerances for utopic
Move qgsfunction to qgis.core.

Add new register_function method when not using decorator
Wrap function call in try block to catch and report errors
[processing] use extent instead of width, height and center in Create
Grid algorithm (fix #11481)
Reform qgis.uitls file
Remove qgsfunction from qgis.utils.

Import from qgis.core so we don't break API
[Expression] Don't unregister function if not registering
travis: irc notification if build status changes
update scripts/fix_allows_to.sh and run it
[Feature] Allow custom expression functions in expression widget
indentation update [ci skip]
[FEATURE] Add comment functionality to QgsExpression
Add block comment tests
Preserve expression formatting