Optimise posts requests

[AFCMS]

Currently:

• Each post details is fetched individually in the post component, categories and profile infos (for the handle), this is inefficient and should be obtained with a join or a view.
• Everything is loaded at once, no request pagination.

[AKArien]

Just to be clear : the client library side has been done as of commit fa2a933
The pages need to switch to using them

[AFCMS]

Some improvements have been done, but it's not quite there.