Add ability to block users and communities (v2)

[krawieck]

add user blocking to

• posts
• comments add community blocking to
• posts add blocks page in settings where users & communities can be unblocked

additionally:

• transitioning of post, post page, and comments to mobx
• sync post with full post

https://user-images.githubusercontent.com/10037914/135691477-7816a979-e8ab-495e-96da-b26d0c30f78c.mov

https://user-images.githubusercontent.com/10037914/135709152-139504c5-8dc5-4778-8aa4-2ecb3133c619.mov

https://user-images.githubusercontent.com/10037914/135709159-427163eb-4fa6-4899-bd67-4dee2cf6bf62.mov

this PR advances #244 but does not close it. there are several things that i'd like to add but i don't want this branch to be too out of sync with master.

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things that i will do in another PR:

• search & block in block page in settings
• block in community page
• block in user page

[krawieck]

fixes #160