Improve documentation (#598, #1105)

Improve documentation (#598, #1105)
 * rework/simplify server configuration/requirements pages (consolidate/simplify SSL/TLS/apache configuration)
 * update index.md introduction
 * remove external images (badges)
 * Fix COPYING link and documentation links
 * Update features list
 * dedpulicate information
 * remove server-requirements.md and move relevant doc to other files
 * TODO: rework nginx configuration (single configuration example, with commented out blocks for special cases)
 * TODO: consolidate download/install/configuration pages
 * remove blank lighttpd configuration section
 * remove Required? column for composer packages, all libraries are mandatory
 * php 7.2 compatibilty
 * clarify that certbot binary and paths may vary depending on install method