Show notifications for new blog posts

Show a notification when a new blog post is received, unless the blog feed is currently visible.

Sub-task of #134 (closed).

Reassigned to @ernir

Added ~14 and removed ~15 labels

Please copy the way this currently works for private messages and forums, we can revisit the overall approach later when we work on #289.

Please add a setting to the settings screen to enable/disable blog notifications, like we have for private messages and forums.

mentioned in issue #289

Started branch 488-show-notifications-for-new-blog-posts

Reassigned to @grote

Added ~11 label

mentioned in merge request !258 (merged)

mentioned in commit 04af39f5

Status changed to closed by commit 04af39f5

Status changed to closed by merge request !258 (merged)

Added ~10 and removed ~14 ~11 labels

mentioned in commit 2577b2ab