Convert to our wrapper class for assertions

* 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 

* Migrate assertions to Webmozart

* Upgrade saml2-library to v4

* Stop considering Issuer-strings

* Stop considering NameID-arrays

* Raise minimum PHP version to 7.0

* Remove tests pre-PHP 7.2

* Upgrade dev dependencies

* Ignore tests for deprecated class

* Add typehints; not touching public API

* Remove none-array replacements-param; old behaviour from pre-1.4 release

* Psalm fixes

* Add upgrade notes

* PSR-12

PSR-12 compliancy

Fix Psalm-issues in the modules-directory

Start migrating to SAML2 getters/setters

Following up on the idea mentioned in #937: If the transport is secure fall back to the `PasswordProtectedTransport` authn context class ref, otherwise keep the current default of `Password`.

Requires a version of the SAML2 library with simplesamlphp/saml2#129 merged due to the reference on a newly defined Constant.

The SAML2int spec suggests that IdPs should advertise two name
identifier formats, and SAML itself supports this. It seems that
SimpleSAMLphp does too, when handling metadata in XML (it is implemented
as an array). However the internal metadata format uses getString,
limiting us to only a single NameIDFormat. So far as I can tell, all
that's needed to fix this is to change the metadata parser to use
getArrayizeString to accept either a string or an array, and to cast
that as a string when necessary.
This may solve issue simplesamlphp/simplesamlphp#91

This resolves #888.