Currently the remember me functionality does not work correctly and using it results in severable undefined index errors as the expire cookie parameter is passed along the SessionHandlerPHP which does not accept this one. Using lifetime instead of expire, effectively doing the same thing, this can be fixed in a pretty simple way. Next to that the params given to the session handler are merged with the current ones before given to the session handler instead of after.

Incorrectly refactored in eb204573

Improve error handling

This reverts commit f1e05f8f.

The previous situation was confusing with various contradicting
(staments of) defaults, mixed with old style and new style
configuration.

Simplify by deciding that having backtraces is so
useful that it is the defaut, both old and new style configurations.
(It was already default on in the config template,
which seems 'canonical'.)

Previously, would show inappropriate precision, like "0.0598134 hours ago"
or "1490532.4129 hours from now" depending on the expiration date.

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.

Convert to our wrapper class for assertions

Check whether http://macedir.org/entity-category is set in the EntityAttributes
before using it as argument in in_array(). This prevents a "TypeError:
in_array() expects parameter 2 to be array, null given" error.

This situation happens when we do have EntityAttributes in the metadata but
none of type "http://macedir.org/entity-category". An example is an IdP
supporting https://refeds.org/category/research-and-scholarship, which would
have "http://macedir.org/entity-category-support" but not per se also
"http://macedir.org/entity-category".

We can remove several tags, login:processing and admin:metaconv_selectfile, and
replace several others with their English text.