Add a "Powered by PHPStorm" link to the footer

As discussed here: https://groups.google.com/forum/#!topic/joomla-dev-cms/-p23OoOi6kA

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From my own personal point of view this is not so much about giving something back. In fact I am using my own (paid) license, even for my community contributions.

It's just to say:
**PHPStorm is a great piece of software and we are using it extensively during the development of the JTracker Application.**
aka "Powered by" - please find some appropriate (short) wording ;)