Merge branch '496-implement-ui-for-reblogging-and-blog-comments' into 'master'

UI for reblogging and blog comments

This MR wraps all blog posts inside a `CardView` and adds a reblog button to blog posts. When this button is pressed, a new activity opens that shows the blog post again and allows the user to reblog it into their own blog. An optional comment can be added.

Also a new compound view `AuthorView` is introduced to display authors and their trust level in a consistent way.

The `BlogController` has been refactored, so the `FeedController` can share most code through an abstract base class.

![reblog2](/uploads/ce4764851c4cbe39684c95a3b427e3a2/reblog2.gif)

Closes #496, #437 

See merge request !300