phpki: code improvements

There are some small changes and interface enhancements to PHPki in 4 commits:
 - New fields on the setup page: allow to adjust CRL distribution points, CA revocation and policy URLs. Very usable if you're using PHPki to manage CA, but distribute your CA data (CRL, revocation check script) on different URL;
 - New fields on the setup page; allow to optionally set certificate comments that will be used in the system during certificate creation instead of PHPki default ones.
 - Request certificate page improvements: show 'IP Addresses/DNS Alt Names' in results for 'SSL server' requests only, fix appropriate fields order, fix text labels, fix 'DNS Alt Names' box visibility after return;
 - Fix policy URL in page headers;
 - Fix 'is_fqdn()' function to support wildcard domains in 'DNS Alt Names';
 - Remove DH params generation during setup stage, they aren't used actually;
 - Keysize setting and usage generalization, e.g. prevent from dealing with 1024bit CSRs, passing and setting parameters with such values anywhere. 2048 bits are used everywhere for more compatibility;
 - Some HTML cleanup.