Follow the suggestions of [draft-knodel-terminology-00](https://tools.ietf.org/id/draft-knodel-terminology-00.html)
and other language frameworks and replace the notion of master/slave
with a more neutral primary/secondary.

Squashed commits:
[090679e6b] authsources must be an array
[1778d0c21] only set the AuthSource if it also exists, but always remove the config
variable.
[c09669e32] add the possibility to specify one AuthSource to be shown and the rest
are used via multiauth:MultiAuth

They seem to cause trouble, also inconsistent behaviour between versions of the memcached extension.

This was available for the memcache extension, but when we moved to memcached it went away since the API is different and required changes. The issue with persitence in memcached is that persistent connections require a common identifier, which shouldn't be fixed. Therefore, we need to change a bit the way the memcache servers are configured in config.php as well.

* Remove deprecated classes

* Remove support for certificate fingerprints

* Remove many deprecated methods and pieces of code

* Remove SAML1.1/Shib1.3 support

* Remove many superfluous annotations

* Update unit test to work with new PHPunit

Closes #1268 
Closes #1020 
Closes #431 
Closes #167 
Closes #151 

Different from the other options, setting it to null does not use
a default but throws an error if you enable metadata signing, so
enabling metadata signing in the default config will throw an
exception. Better to just leave it out, the option is documented
but should not be necessary for most installs, so needs not be
in the template.

Add support for RFC6265bis SameSite cookie attribute

* Update simplesamlphp-theming.md

* Add theme.controller config setting

Break with MS AD

This introduces a "theme.header" configuration option in order to achieve that.

Twig will always use gettext, legacy will use legacy. Twig does not
work with legacy so new ui would break if you would not also set this
option. Instead, just switch the system in use based on the usenewui
config variable.