Don't clear non-SuckerPunch actors from registry

[malandrina]

• Currently SuckerPunch::Railtie clears all actors from the Celluloid actor registry during initialization. This is problematic because an application using SuckerPunch may have additional Celluloid actors.
• In this commit I propose prefixing the names of SuckerPunch actors such that we can ensure the Celluloid registry is cleared only of SuckerPunch actors on application initialization, per @nullstyle's suggestion here: https://github.com/brandonhilkert/sucker_punch/issues/99
• Update SuckerPunch::Queue#name to add a prefix to queue names
• Introduce SuckerPunch.clear_actors
• Update SuckerPunch::Railtie to use SuckerPunch.clear_actors

[malandrina]

@brandonhilkert great feedback, thank you! I'll let you know when I've made the changes, should be over the next couple days.

[malandrina]

@brandonhilkert this is ready for another look when you have some time.

[brandonhilkert]

:+1: Thanks again! Nice work!

[malandrina]

No problem! Thanks for the opportunity.