* Add support for U2F

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Add vendor library
Add missing translations

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Minor improvements

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Add U2F support for Firefox, Chrome (Android) by introducing a custom JS library
Add U2F error handling

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Add U2F login page to OAuth

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Move U2F user settings to a separate file

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Add unit tests for u2f model
Renamed u2f table name

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Fix problems caused by refactoring

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Add U2F documentation

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Remove not needed console.log-s

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Add default values to app.ini.sample
Add FIDO U2F to comparison

Signed-off-by: Jonas Franz <info@jonasfranz.software>

* Cleaning up public/ and documenting js/css libs.

This commit mostly addresses #1484 by moving vendor'ed plugins into a
vendor/ directory and documenting their upstream source and license in
vendor/librejs.html.

This also proves gitea is using only open source js/css libraries which
helps toward reaching #1524.

* Removing unused css file.

The version of this file in use is located at:
  vendor/plugins/highlight/github.css

* Cleaned up librejs.html and added javascript header

A SafeJS function was added to templates/helper.go to allow keeping
comments inside of javascript.

A javascript comment was added in the header of templates/base/head.tmpl
to mark all non-inline source as free.

The librejs.html file was updated to meet the current librejs spec. I
have now verified that the librejs plugin detects most of the scripts
included in gitea and suspect the non-free detections are the result of
a bug in the plugin. I believe this commit is enough to meet the C0.0
requirement of #1534.

* Updating SafeJS function per lint suggestion

* Added VERSIONS file, per request