[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
QgsExpression: some const fixes
Add line comments to QgsExpression

Delimited by double-minus and EOL/EOF

Example:
  $id -- This is the feature id
Change unary minus test --1 to -(-1)

See http://lists.osgeo.org/pipermail/qgis-developer/2014-November/035835.html
[processing] fix Convex hull algorithm (fix #11725)
[processing] fix GRASS output parser (fix #10660)