improving article display, improving style (updating theme)

- ported the project to [Android Studio](http://developer.android.com/sdk/installing/studio.html) (better building system, better editor)  
- articles are stored with their original HTML (as it was stored as plain text)  
- use a webView with stylesheets to display the articles (+ working images, +working links ...) (used stylesheets from iOS app)  
- replaced "In the poche" with "wallabag" in all images and text occurrences  
- improved layout (latest theme for ~ every Android Version)