Added configurability of admissible language at the contest level.
Honor the language restrictions in the contestant's interface.

Also changed the unit tests root directory's name to avoid collisions
of import names.
Correct return values for all services.
Added Python to the supported languages.

Currently only tested for batch task types. Documentation needs to be
updated.
Reorganized functional tests in sections.
Functional tests for OOM solutions.
isolate: Update from https://github.com/NZOI/moe-cms/commit/ee98549208e24ab9e4c1ce414c09c202f96d8405

drop root privileges, use real user id to open metafile - security issue - can be used for privilege escalation attacks for users permitted

close metafile to prevent box_inside writing false data to it - see https://github.com/ronalchn/isolate-cheater
Install isolate without o+x mod.

This will help mitigate the effect of future security bugs.
Install isolate with group assigned to cmsuser.

Otherwise no one is allowed to run it besides root.
Removed obsolete GerImporter

WARNING: cmsReimporter doesn't touch test submissions
Replaced BlockString
Global is evil
Removed LoaderConfig
Removed use_lib parameter (always add the standard include directory)
Merge remote-tracking branch 'upstream/master' into ger-taskformat