WebIntent phonegap 2.7.0 compat

The depreciation of Plugin in favor of CordovaPlugin and the add of CallbackContext broke the WebIntent code.
I couldn't find anywhere a WebIntent version supporting phonegap 2.7.0.
Here is a version that does work with 2.7.0.

Note: This is badly coded, java is not my specialty but it works.
Note2: You can ignore commits about launchActivity. It's a special feature i need to start an other app from phonegap.