Add component.json to allow simple installation through Bower

Component.json was added, to allow installation through [Bower](https://github.com/twitter/bower).

Dependency to jquery 1.7.1+ is defined here.

If you merge this, please also tag then the current HEAD as "0.0.1" (the same version as in component.json), so dependencies to this specified jquery-dropdown version could be defined. (And the version as well as new tag should be increased once new version is released.)