* Introduce user display names
It is not uncommon for forums to be intergrated with sites where users
don't have a unique "handle" - they might just have their first name,
or a full name, which is not guaranteed to be unique.
This commit introduces the concept of "display names" for users. By
default display names are the same as usernames, but extensions may
override this and set them to something different. The important thing
is that all code should use `display_name` whenever intending to output
a human-readable name - `username` is reserved for cases where you want
to output a unique identifier (which may or may not be human-friendly).
The new "GetDisplayName" API is probably sub-optimal, but I didn't worry
too much because we can come up with something better in `next-back`.
ref #557
* Apply fixes from StyleCI
[ci skip] [skip ci]
Currently all of a post's replies are loaded in full whenever the post
is loaded, which is kind of overkill - we really just need to know that
they exist (and who posted them) in order to render the "X replied to
this" line.
This is useful for forums integrating with an external website (eg. a
WordPress site), so they can reference existing avatars directly.
For alternative storage locations (eg. S3) the best practice will still
be to store a relative path and then configure an external base "assets
URL" (this is not currently possible - TODO).
Given this change, I think it would probably make sense to rename the
column to `avatar_url` in the upcoming batch of database naming changes
- then it can contain either a relative or an absolute URL -
@franzliedke do you agree?
