Fix/assign quantifiers only once

[mattyg]

Short-term workaround to reduce risk of https://github.com/commonsbuild/praise_frontend/issues/101
Resolves https://github.com/CommonsBuild/praise_frontend/issues/101 -- I created a new ticket #223 to consider more "ideal" solutions.

Overview

• (merged feat/per_period_settings to avoid a tricky merge later)
• created utilily function verifyAnyPraiseAssigned() to check if any praise within a given period has already been assigned to quantifiers
• modify period controller assignQuantifiers to throw an error if any praise has been assigned for the period.

[kristoferlund]

Nice! And yes, lets make sure we have a more waterproof way to handle concurrent api calls etc in the future.