Autodetect version of MythbuntuPPA for supported Ubuntu release

I've added a library to support the autodetection of 
the latest supported version of mythtv for any given 
release of Ubuntu.  The default recipe now uses this 
and the `apt_repository` LWRP from the [apt cookbook][1] 
to add the correct PPA.  This should work for all cases 
and fix an issue where `python-software-properties` was 
not already installed (and therefore `apt-add-repository` 
was not available).

I've also made significant improvements to the unit 
and integration testing framework for this cookbook.
Travis-CI is now available for use with testing changes to 
this cookbook.  If you'd like to add this to your repo, 
simply follow steps 1 and 2 [here][2].
For detailed description of my changes see below:

Changes
=======


* Expand supported versions of Ubuntu:
  * Intelligently detect the latest version of MythbuntuPPA/mythtv to use based on LSB codename
  * Added MythbuntuPPA library (+rspec tests) for mapping supported platform versions to PPA versions
  * Use apt\_repository LWRP from apt cookbook to add the PPA
* Added cookbook test framework
  * Added chefspec, serverspec, test-kitchen tests (Run via: `rake` or `strainer test`)
  * Use knife cookbook test & foodcritic for linting
  * Use RallySoftware-cookbooks/cookbook-development cookbook test framework gem
  * Added more supported versions of ubuntu to test-kitchen platforms
  * Use [Travis CI](http://travis-ci.org) to automatically run tests for pull-requests & changes to this cookbook
* Minor enhancements
  * Fix metadata
  * Fix Foodcritic warnings: FC007, FC019
  * Cookbook version now specified in VERSION file


[1]: https://github.com/opscode-cookbooks/apt#apt_repository
[2]: http://about.travis-ci.org/docs/user/getting-started/