Change all license headers to comply with REUSE specification.

Fix #16132

Co-authored-by: flynnnnnnnnnn <flynnnnnnnnnn@github>
Co-authored-by: John Olheiser <john.olheiser@gmail.com>

Why this refactor

The goal is to move most files from `models` package to `models.xxx` package. Many models depend on avatar model, so just move this first.

And the existing logic is not clear, there are too many function like `AvatarLink`, `RelAvatarLink`, `SizedRelAvatarLink`, `SizedAvatarLink`, `MakeFinalAvatarURL`, `HashedAvatarLink`, etc. This refactor make everything clear:

* user.AvatarLink()
* user.AvatarLinkWithSize(size)
* avatars.GenerateEmailAvatarFastLink(email, size)
* avatars.GenerateEmailAvatarFinalLink(email, size)

And many duplicated code are deleted in route handler, the handler and the model share the same avatar logic now.

* Decouple TestAction_GetRepoLink and TestSizedAvatarLink.

* Load database for TestCheckGPGUserEmail.

* Load database for TestMakeIDsFromAPIAssigneesToAdd.

* Load database for TestGetUserIDsByNames and TestGetMaileableUsersByIDs.

* Load database for TestUser_ToUser.

* Load database for TestRepository_EditWikiPage.

* Include AppSubURL in test.

* Prevent panic with empty slice.

Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

* add `/assets` as root dir of public files

Signed-off-by: a101211279 <1012112796@qq.com>

* move serviceworker.js

* make fmt

* fix some link

* fix test

* Apply suggestions from code review

Co-authored-by: silverwind <me@silverwind.io>

* Apply suggestions from code review

Co-authored-by: silverwind <me@silverwind.io>

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: zeripath <art27@cantab.net>

* Direct avatar rendering

This adds new template helpers for avatar rendering which output image
elements with direct links to avatars which makes them cacheable by the
browsers.

This should be a major performance improvment for pages with many avatars.

* fix avatars of other user's profile pages

* fix top border on user avatar name

* uncircle avatars

* remove old incomplete avatar selector

* use title attribute for name and add it back on blame

* minor refactor

* tweak comments

* fix url path join and adjust test to new result

* dedupe functions