Limit rate of solution processing #31
Description
The current implementation limit the number of concurrent verification but allow a new verifier to start as soon an other one stops. It's not flexible enough. Instead it be refactored to:
- limit the number of concurrent verification per language; the python or node container are easier to run than the java.
- limit the number of verifier per sec.
- allow burst.
It could use a token bucket algorithm and require the java verifier to acquire more token before starting.