testing of core:AttributeLimit

remove src_dir from .coveralls.yml

this was added to fix a bug - now we need to remove it :-)

sqlite3 tests require the ext-sqlite3 module

This used to work in old phpunit - but not the version on travis-ci

test core:AttributeLimit - since array can only contain int and string
I can’t raise the non covered constructor exception.

changed the extension on the request of @thijskh

add sqlite3 as a dev dependency. you might not notice this when running
tests locally otherwise.

Avoids:
ERROR 1170 (42000): BLOB/TEXT column 'uid' used in key specification without a key length

Minor optimalization - Don't gather settings if we don't use them

Don't gather the proxy.auth setting if we don't use it

Feature/proxy auth

This will invoke a more convenient on screen keyboard on mobile
devices and give some syntax validation as a bonus.

Try with "composer update" instead of "composer install". The latter does not support --prefer-lowest.

Since this branch is now officially released we need to support it.

* Remove 404 link to SSP news; this is covered on simplesamlphp.org now.
* Make screenshots link relative, so docs don't trigger insecure
  content warnings.
* Compress png images.

Fix/keep empty folders