* add check_mode option for tasks
includes example testcases for the template module
* extend check_mode option
* replace always_run, see also proposal rename_always_run
* rename always_run where used and add deprecation warning
* add some documentation
* have check_mode overwrite always_run
* use unique template name to prevent conflicts
test_check_mode was right before, but failed due to using the same filename as other roles
* still mention always_run in the docs
* set deprecation of always_run to version 2.4
* fix rst style
* expand documentation on per-task check mode
