[HTTPS-Everywhere] Rules not loaded until website is visited

[Jacob Hoffman-Andrews]

> It might be the best idea: am I correct in believing you were thinking about
> loading the list only when requested? Meaning that we query the list
> directly in the sqlite DB when somebody is using the "Enable/disable" menu?

To be a little more precise - we already preload the list of host
target patterns (e.g. "*.eff.org"), but not the rulesets. This change
would match against the host patterns and then load from the sqlite DB
any that weren't already loaded.

The search would then be done against the in-memory list of host
patterns, which includes user-generated rules.