Add sakai.property to disable Forums Ranks feature - Phase 1: disabling the Ranks page

Because of the performance issues (SAK-29654) with the new Forum Ranks feature that we got in Sakai 10 (SAK-24854), we had to create a property to disable the Ranks system to avoid our database from crashing under the hundreds of thousands of queries per hour and the millions of CPU-intensive buffers each hour attribute to the Ranks feature.

However, because of the lack of time over the summer, we decided to implement this property in two phases:

Phase 1 - disable the Ranks page from the UI so that instructors and maintainers cannot add Ranks (this ticket)

Phase 2 - disable the Ranks feature throughout the code (SAK-29936)

This ticket will contain the patch for Phase 1.

Introduces sakai.property:
msgcntr.forums.ranks.enable=true (default)