PSR-12 compliancy

Allow the new major version to be used as well (lock-file remains at 3.x)

Can be removed for 2.0, or when the negotiate-module is no longer included in the release

* Allow list of entity ids to be loaded to better support idpList

Certain metadata sources, like mdq, were don't support loading all metadata which
prevented them from being used with idplist. This change adds support for allowing
metadata sources to load a list of entities, allowing MDQ to be used for idp list.

Downgrade externalized modules to a version that doesn't hold BC-breaking Webmozart-assertions

* Externalize ldap

* Remove tests for LDAP-module

* Redirect old LDAP-class to ldap-module for backwards compatibility

* Externalize negotiate

* Install pecl-krb5

We need to include this in our travis-tests as long as we include the negotiate-module in the release

* Externalize consent module

* Update Psalm

* Ignore DocblockTypeContradiction and RedundantConditionGivenDocblockType

* Fix Psalm-errors

* Raise minimum PHP-version to 5.6

* Update lock-file accordingly

* Fix phpunit

* Suppress Psalm-issue

The old mail class uses the built-in `mail` function in PHP, and builds a payload by itself using hard-coded HTML and MIME-snippets. Let's use a library for that; PHPMailer has new dependencies and does all the heavy lifting.

Also reorder alphabetically

Deprecation warning: require-dev.mikey179/vfsStream is invalid, it should not contain uppercase characters.