Fixed #2806 Rewrote session management system

Session system sets and manages its own cookies to identify sessions.

Features high-entropy session IDs (issue #2964), encrypted session unlocking where switching from HTTPS to HTTP will use a seamless bounce-back to HTTPS and back again to HTTP while trying to maintain POST requests (issue #3038) stronger session encryption key generation.

Invalidates all PHP session compatibility issues reported (#2655, #2806, #3042)
Fixed session loading parameter handling
Fixed session() access and session loading/preloading

A "preload" loads a session created before (pre-) the current one. The load() method needs to set the session property after load.
Merge branch 'feature/session-rewrites'