Make metarefresh work in 1.17.0 rc1

Fixed typo introduced by #1008

Fixes a typo introduced by #906

* Autoloader infinite recursion fix

Fixes simplesamlphp/simplesamlphp#1030

* Added test to ensure old autoloader behaviour is preserved

Also fixed undefined variable notice

Added Slovenian remember translations

Added slovenian processing translation

added slovenian consent abort translation

* Update simplesamlphp-theming.md

* Add theme.controller config setting

class_implements() returns class names without leading backslash

Items in $warnings should either be a string or an array with two values

* Correct xh translations issue #1022

These assets have been moved somewhere else or integrated as part of the new build system, so they are no longer used / necessary.

Before calling npm to install dependencies and build, we need to step into the installation directory. Also, node_modules and the stylesheet.js* byproduct can be removed in production.