Issue #2898045 by colan: Added the admin selector for choosing the CA signature verification plug-in.

drupal generate:plugin:type:annotation --module="certificatelogin" --class="CaSignatureVerificationPlugin" --machine-name="certificatelogin.ca_signature_verification" --label="Certification Authority Signature Verification"

Issue #2854922 by colan: Added config settings for the server's cert variable & the CA to verify against.

Reg Proctor authored Sep 23, 2015 and Jyri-Petteri Paloposki committed Sep 23, 2015

Issue #2572935 by Reg: Strict warning: Only variables should be passed by reference certificatelogin_user_identities line 134 certificatelogin.module

Fix a bug where the 7.x version didn't work unless an old variable no longer in admin view is set.

Issue #1682726 by crontab: ”Present login link on access denied (403)” didn't pre-select the current value.

Adding maintainer contact info to README; removing unnecessary PHP requirement; adding module package info