luci-base: load luci preferences early

luci-base: load luci preferences early

Follow-up to 315dbfc7498e2f43afb0119b992915e8f311bc37

In order to look at any saved uci value, the luci config
must be loaded before we render the page, so we can determine
stored preferences, for things like table filter, without
encumbering all consumers of configurable elements to load
the luci uci configuration.

All (Table) elements extend CBIAbstractElement, so load
there.

Signed-off-by: Paul Donald <redacted>