"More visibility options" for site posts

[boonebgorges]

See http://redmine.citytech.cuny.edu/issues/3281

The City Tech OpenLab has built a feature that adds a 'More visibility options' to the block editor. This feature allows a specific post on a public site to be limited to group members only, or to network members only. Here's what it looks like on that site:

We should add this to CBOX OpenLab. The language will likely need small changes:

• The screenshot says "Only logged-in members of this Course can see this post. This will override the Public visibility setting above.". It's difficult to build a sentence like this with variable group-type names and between languages. So instead we'll need something like "Only logged-in members of this site can see this post...". On CBOX OpenLab, site and group membership is linked.
• Instead of "Only logged-in OpenLab members can see this post", better to say "Only logged-in members of the network can see this post", or simply "Only logged-in users can see this post".

[boonebgorges]

This is mostly ported over. The missing piece is the blocking that happens in the activity stream. On the City Tech OpenLab, this piggy-backs on how activity-stream blocking works for private group memberships. So I'll wrap this ticket when I've ported #469.

[boonebgorges]

The activity privacy toggling has now been introduced.

[bree-z]

We would also like to include functionality added in http://redmine.citytech.cuny.edu/issues/3382:

• The 'More visibility options' section of the block editor (#3281) should appear on sites with visibility "Visible only to registered users of this network" (value 1; it currently appears only for values 0 and 1)
• The 'Everyone' option should not be available on sites with blog_public=-1
• 'OL members only' should be the default for new posts, again only on those sites with blog_public=-1

Thanks!

[boonebgorges]

This is ready to test.