Customizable submission rate-limit for each module

[BorysekOndrej]

Currently there is a hard limit of 20 submissions per 24 hours per user per module.

Sometimes modules are used as a helping tool for participants to validate their syntax. Currently only the programming module knows two modes - Spustit and Odevzdat. Therefore if text module is used for syntax validation, the rate limit applies.

Having a customizable limit (for example using module.json files would be nice to have.