Don't specify file size limits for submissions (and usertests) in cms.conf

At the moment there's a field called max_submission_length in cms.conf that globally determines the maximum size for submitted files. That is, the limit applies to all files for all tasks of all contests. Also, for example, to the files of output-only tasks, that are actually outputs and could be really large.

I suggest to remove this field and to think of (and implement) a system (i.e. a protocol of communication between TaskTypes, ES, CWS, etc... that somehow extends submission_format) that allows the TaskTypes to specify these limits on a per-task and even per-file basis. They could even be made configurable through task_type_parameters.

A special note for inputs for UserTests: TaskTypes could specify some kind of formats for these files too, to allow more flexibility (setting a different number, with different names, custom sizes, etc...).

Start with cms.conf and the max_submission_length setting, then trace how submission_format and UserTest inputs are communicated among TaskTypes, ES, and CWS. Review task_type_parameters and the handling of output-only files. Done means replacing the global limit with a defined per-task and per-file mechanism, including flexible UserTest input limits.