feat #1015 Check Git commit message during Travis build

This commit enables checking if commit message of the latest
Git commit is of good length (not too short, not too long) and if it
adheres to certain team's conventions.

To quickly verify the commit message locally, after the commit, the
developers can use `grunt git` command in their shell (if they have
Grunt installed globally).

This commit also provides a commit-time Git hook that can be installed
using this one-liner in the root folder of AT:

 npm install -g grunt grunt-commit-message-verify; cp ./hooks/* ./.git/hooks/

Close #1015.