NOTE: this commit only updates the english section

Signed-off-by: Jan Breuer <jan.breuer@jaybee.cz>

Commit 7bb4d610e5 tries to take the app_name from the locale, however, it is a user defined setting. This causes the app name to simply display as `app_name` instead of the correct value.

templates/helper.go automatically injects the AppName variable into every template, so we can safely use that instead.

Signed-off-by: Daniel Derzsi <daniel@tohka.us>

Would it make sense to actually use the configured app name on the home page?

.. rather than a gogs one

* fix homepage docs link broken

* fix homepage docs links after docs updated

* 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

Conflicts:
	modules/setting/setting.go

Conflicts:
	templates/repo/release/list.tmpl
	templates/user/dashboard/dashboard.tmpl

Conflicts:
	routers/repo/setting.go

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.

add /login and /sign-up link for user signing
fix typo error