Change documentation from recommending 2048 bit keys to using 3072 bit
keys.

Given that we're recommending people generate ten-year keys, 2048 bit
keys are probably a bit short. Almost all commercial certificate
authorities now recommend 4096 bit keys, and eduGAIN requires 3072 bit
keys for new federations.

This change aligns the SimpleSAMLphp documentation with the lower
eduGAIN requirement, since that still meets most standards bodies
recommendations for 2028 (ten years from now). cf
https://www.keylength.com/

Closes: #177

Remove last use of experience icons theme so we can remove it after the old templates have been removed.

Extend @mapgrady's patch for simplesamlphp/simplesamlphp#498 to allow Scoping to be disabled on a per-idp basis as well as globally

Now we can test properly the controllers executing old code.

*    Updated the phpDoc comments to match the code
*    Added return statements
*    Added return values