This makes sure the provided extension ID is a valid id before
initializing it in the extension manager.

The internal lang and localized variables of a plugin are no longer
accessible from the outside. This adds a proper setter and also fixes
the type hinting in the config plugin.

this fixes another problem with our tests and phpunit 6.1

This should fix some tests on PHP 7.1. The work is far from done, we
still have a lot of variables without proper accessibility defined.

* Updated remote.php

Updated remote.php for retrieving all the acl details.

* Updated remote.php

By mistake changed in addAcl instead of listAcls.

Those tests either just check that an exception is NOT thrown or are
there to check dependencies for other tests. Newer phpunits mark all
tests as risky that have no assertion.

squashed a whole bunch of PRs

closes #1907
closes #1908
closes #1909
closes #1910
closes #1911
closes #1912
closes #1913
closes #1914
closes #1915
closes #1916
closes #1917
closes #1918
closes #1919
closes #1920
closes #1921
closes #1922

ran svgo over all the admin svg files to strip all unneeded cruft.

using icons from https://materialdesignicons.com/