Add support for comments and reblogging to Blog Client
Comments and reblogs need to depend on the post they refer to. Since message dependencies are limited to one group, the post and also the comments need to be wrapped when commented on or reblogged to another blog (and group).
For this reason, in addition to comments, two new wrapping message types are introduced. They retain all data of the original messages and allow for reconstruction and signature verification.
This MR breaks backwards compatibility with old blog posts. It removes the content type, title and parent ID from the post.
Furthermore, it includes one commit that replaces the
MessageSharedEvent with a
Closes #494 (closed)