Enableself.log in most functions.

[tchaton]

What does this PR do?

This PR re-enables logging in most of callbacks and models functions while retaining some speed behind efficient.
We don't support logging in batch_start function to save 0.5 % of the entire training_epoch time.

Fixes #4857

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[codecov]

Codecov Report

Merging #4969 (2bc49bf) into master (9b1afa8) will decrease coverage by 0%.
The diff coverage is 96%.

@@          Coverage Diff           @@
##           master   #4969   +/-   ##
======================================
- Coverage      93%     93%   -0%     
======================================
  Files         129     129           
  Lines        9363    9371    +8     
======================================
+ Hits         8681    8688    +7     
- Misses        682     683    +1     

[SeanNaren]

few nits but lgtm