Reimplment >= competitor limit check

[dunkOnIT]

Previous version of this PR was reverted, as it triggered an error in live environments where Redis only returns strings

[FinnIckler]

wca-registration/app/controllers/registration_controller.rb

Line 31 in 3f7c7e8

render json: { count: Registration.accepted_competitors_count(competition_id).to_i }

Here I just use .to_i not sure what is better

[FinnIckler]

Anyway how you implement it, you should remove the to_i from my line

[FinnIckler]

@dunkOnIT please fix the conflicts and remove the to_i where Registration.accepted_competitors_count(competition_id) is called elsewhere