context_help/function_help:
- remove en_US postfix
- remove translated files (translation were moved to ts files earlier)
- remove unused jQuery (python help doesn't use it anymore)
- change expression label in QgsQueryBuilder and add context help (partly fixes
  #8129)
german translation update
Update
Fix for #7927 : Add a warning message if trying to print a composer as an image fails (Qt's QImage sanity check for memory overflow)
Fix #7927 : Add a warning message if trying to print a composition
as an image fails (Qt's QImage sanity check for memory overflow)
Moved previous commit from core/qgscomposition to apps/qgscomposer
as QGIS server uses qgscomposition.