* Refactor `i18n` to `locale`

- Currently we're using the `i18n` variable naming for the `locale`
struct. This contains locale's specific information and cannot be used
for general i18n purpose, therefore refactoring it to `locale` makes
more sense.
- Ref: https://github.com/go-gitea/gitea/pull/20096#discussion_r906699200

* Update routers/install/install.go

There are multiple places where Gitea does not properly escape URLs that it is building and there are multiple places where it builds urls when there is already a simpler function available to use this.
    
This is an extensive PR attempting to fix these issues.

1. The first commit in this PR looks through all href, src and links in the Gitea codebase and has attempted to catch all the places where there is potentially incomplete escaping.
2. Whilst doing this we will prefer to use functions that create URLs over recreating them by hand.
3. All uses of strings should be directly escaped - even if they are not currently expected to contain escaping characters. The main benefit to doing this will be that we can consider relaxing the constraints on user names and reponames in future. 
4. The next commit looks at escaping in the wiki and re-considers the urls that are used there. Using the improved escaping here wiki files containing '/'. (This implementation will currently still place all of the wiki files the root directory of the repo but this would not be difficult to change.)
5. The title generation in feeds is now properly escaped.
6. EscapePound is no longer needed - urls should be PathEscaped / QueryEscaped as necessary but then re-escaped with Escape when creating html with locales Signed-off-by: Andrew Thornton <art27@cantab.net>

Signed-off-by: Andrew Thornton <art27@cantab.net>

close #14822

* Unexport SendUserMail

* Instead of "[]*models.User" or "[]string" lists infent "[]*MailRecipient" for mailer

* adopt

* code format

* TODOs for "i18n"

* clean

* no fallback for lang -> just use english

* lint

* exec testComposeIssueCommentMessage per lang and use only emails

* rm MailRecipient

* Dont reload from users from db if you alredy have in ram

* nits

* minimize diff

Signed-off-by: 6543 <6543@obermui.de>

* localize subjects

* linter ...

* Tr extend

* start tmpl edit ...

* Apply suggestions from code review

* use translation.Locale

* improve mailIssueCommentBatch

Signed-off-by: Andrew Thornton <art27@cantab.net>

* add i18n to datas

Signed-off-by: Andrew Thornton <art27@cantab.net>

* a comment

Co-authored-by: Andrew Thornton <art27@cantab.net>

* make repo as "pending transfer" if on transfer start doer has no right to create repo in new destination

* if new pending transfer ocured, create UI & Mail notifications