* allow current user to reset their own password

* handle reset password edge cases properly and consistently

* remove dangling assignment

* properly label account recovery instead of reset password

* remove 'Click here' from button

* update English-only account-recovery templates

* Make distinction between DisplayName and Username in email templates

Store the actual username in the variable named Username and store the
separate DisplayName in another variable. This allows us to access the
actual username when we need, which currently fails if a user has set a
full name.

Fixes #6161

* Use u.Name directly

No need for extra function, also change use in all mail sending
functions here

* Don't include Username when not used

This solves the problem of administrators creating accounts for users
that then do not know their initial password (without the administrator
sending it to them via some other channel).

* xxx_active_code_live setting in printed in hours and minutes instead of just hours

* Update app.ini description of xxx_code_lives settings

* Added rel="noopener" to target="_blank" hrefs

* Replaced gogs.io/docs with docs.gitea.io

This commit improves templates readability, since all of them use consistent
indent with all template command blocks indented too.

1. Indents both HTML containers such as <div>, <p> and Go HTML template blocks
   such as {{if}} {{with}}

2. Cleans all trailing white-space

3. Adds trailing last line-break to each file

- #1496: fallback plain text
- #1002: add date header
- #913: fix encoding of header

Removed trailing whitespaces with

```sh
for file in `grep -r " $" * | cut -d : -f 1 | sort | uniq | grep -v " "`; do sed -i 's/[ \t]*$//' $file; done
```

and some handwork.