Updated license information and readme to be compatible with Dynatable license

Hi there. Firstly, I just want to thank you for your support of dynatable, it's greatly appreciated! I just wanted to let you know that since this library packages the dynatable code, the [MIT license chosen](https://github.com/ricardodovalle/jquery-dynatable-rails/blob/6abd90d030417bb7ac8962d522e2d3c100eecda8/LICENSE.txt) is incompatible with the [AGPL license](https://github.com/alfajango/jquery-dynatable/blob/ce207ab5070bf6bf5482d9b4178b2b1b7cc88c98/LICENSE.txt) used by dynatable. If you could update the library to also use the AGPL or other compatible license, that would be great!

Also, as someone how has gone through the due diligence process surrounding a Rails application, one of the most tedious jobs is verifying that the open source code you've used in your project is licensed properly to allow transfer of ownership and use within the project. Generally the first thing I do is look through the Gemfile and check the licenses of all the gems, which often package other open source code, such as this one. It makes it a much more tedious job when I can't assume that the authors of those libraries have compatibly licensed their code with those of the code they've packaged. Since changing licenses in a project generally still means that any old versions retain their respective licenses, you may consider putting a note in the Readme that lets people know that the old MIT license was incompatible and could not be considered accurate.

Going forward, you may also consider including a note like the one in the [hicharts-rails gem Readme](https://github.com/PerfectlyNormal/highcharts-rails/blob/451e30e31390fabda6d14686bb284b094caf5bfd/README.markdown) letting people know that if the AGPL license is not sufficient for their needs, they may obtain their own license with Dynatable directly.

Sorry for the wall of text. I made a pull request with the requested changes to make it easier. Thanks again for your support!