Remove Cache::settings

It doesn't appear to be necessary and is confusing to have both:

    Cache::config
    Cache::settings

with different purposes.

Replaced the greedy retrival of instance config (static::settings) with
calls to `$engine->config()` before use.
populate defaultConfig in all cache adapters

Remove the duplicate document block from `Cache` as it will most likely
get out of sync with Core cache engine config (it is already out of
sync, missing keys).

Sort all the keys in defaultConfig so that it's easier to fine keys/see
differences.

Remove defaults from the docblock for the defaultConfig property - it
will only duplicate the actual property value and most likely get out of
sync.