Added bower.json

A bower.json file to make easy the library to be used in bower based projects. To use it:

bower install git://github.com/heigeo/leaflet.wms.git#gh-pages

If you want to release your library to the bower repository execute this:

bower register leaflet.wms git://github.com/heigeo/leaflet.wms.git

You need to create a "SemVerTag" (Vx.y.z) that has to be equals as the version in the bower.json