Make the repository a functioning Cordova project

"Functioning" here means building and running; at this point, file
opening and offline storage do not work (at least on Android).

The required plugins are:
* fr.smile.cordova.fileopener 1.0.0
* org.apache.cordova.device 0.2.10
* org.apache.cordova.file 1.2.0
* org.apache.cordova.file-transfer 0.4.4

A future commit will provide a way to manage plugin dependencies.
Start over, ready for the next version of the app