Potential bug in NormalizedShannon and NormalizedRenyi

[gallardoalba]

Base Shannon and Renyi indices restrict to the top 2 isoforms but their normalized counterparts were using all isoforms with a log(n) divisor, breaking the expected NormalizedShannon = Shannon / log(2) relationship.

• Fixed by applying the same top-2 restriction to NormalizedShannon and NormalizedRenyi and normalizing by log(2) instead.
• Default thresholds updated from 0 (which classified everything as polyform) to 0.500/log(2) and 0.435/log(2).
• Added value-equality tests to lock in the relationship, and uncommented the previously disabled RunDIV tests for these indices. Affects GetDiversity.R, RunDIV.R, and their tests.