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, the developers can use
`grunt git` command in their shell (if they have Grunt installed
globally).

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(this is a preview, the grunt plugin needs some unit tests before merging this)