chore(log): Convert `elgg_log` to OO equivalent in all classes
feature(php): Require PHP 5.4+

PHP 5.3 is currently end-of-life and 5.4 will have only ~1 year of security patches
when Elgg 1.10 is scheduled to be released.

Fixes #7090
Merge pull request #7475 from ewinslow/php-54

feature(php): Require PHP 5.4+
Merge pull request #7473 from ewinslow/oo-services-logger

chore(log): Convert `elgg_log` to OO equivalent in all classes
chore(cache): Add some nice new internal APIs for caching