chore(travis): Added travis script to check commit messages for commit ranges. Updated travis.yml.

Fixes #6381
Refs #5976
chore(git): Improved commit message script when being used as git hook.
chore(travis): Broke out the commit message validator into a class to make it testable.

Added tests for the git hook script and the travis script.
chore(docs): Updated best practices to include commit message reqs.