[content hub] Enhance content hub sharing screen

Some of the content hub sharing screen might need to be reviewed by design and possibly refined since they were not part of the effort when those were created.

Here is a screenshot (attached) of the current UI for facebook, twitter etc. sharing.

The usual flow is:

- the user is in the gallery app (as a typical resource sharing app),
- the user decides to share a picture and clicks on share,
- the user selects a webapp, and then the webapp is launched,
- the attached screen is launched automatically so that 1. the image can be quickly seen, 2. additional comments can be added to the "post",
- the user clicks post,
- the webview is loaded and refreshed,