Added check availability module.
Changed from list to set for a bit higher efficiency.
Integrated check availability module into availability module, deleted check availability module.
Made some fixes so that link from manage page works.
Merge pull request #422 from uakfdotb/issue406

Added check availability module.
Merge branch 'main-proposed' into main

Merge pull request #422 from uakfdotb/issue406

Added check availability module.

The pull request was accidentally merged into the incorrect branch.