Add some support for comment visibility, fix#217
This add a new column to comment, denoting if they are public or not, and a new table linking private comments to those allowed to read them. There is currently no way to write a private comment from Plume.
Git is having a hard time what happened in Comment::from_activity, but most of it is just re-indentation because a new block was needed to please the borrow checker. I've marked with comments where things actually changed.
At this point only mentioned users can see private comments, even when posted as "follower only" or equivalent.
What should we do when someone isn't allowed to see a comment? Hide the whole thread, or just the comment? If hiding just the comment, should we mark there is a comment one can't see, but answers they can, or put other comments like if they answered to the same comment the hidden one do?
Use uri! to generate links instead of hardcoded urls
Fix#110
Fix invalid links needing to be POST forms
Translate login message for boost and like directly from template
Put js for search in its own file
All the template are now compiled at compile-time with the `ructe` crate.
I preferred to use it instead of askama because it allows more complex Rust expressions, where askama only supports a small subset of expressions and doesn't allow them everywhere (for instance, `{{ macro!() | filter }}` would result in a parsing error).
The diff is quite huge, but there is normally no changes in functionality.
Fixes#161 and unblocks #110 and #273
