This is a first step for #42. Since most access to the scraper classes
is through instances, modules can now dynamically override url and name
(name is now a property).
This is modeled parallel to the "adult" feature, except the user can't
override it via the command line. Each comic module can override the
classmethod getDisabledReasons and give the user a reason why this
module is disabled. The user can see the reason in the comic list (-l or
--singlelist) and the comic module refuses to run, showing the same
message.
This is currently used to disable modules that use the _ParserScraper if
the LXML python module is missing.
