Plugin Support

[cretz]

This issue is kinda a catch-all for plugins. Some quick thoughts:

• Need a more stable ABI before exposing or we need to only expose certain pieces
• Essentially a DLL that can use all the Qt it wants
• There is no plugin store or plugin vetting process, if you use a plugin you are basically giving the plugin dev full rights over everything. We don't have the bandwidth to be the jury here.
• Would of course need a plugin init that does version check and what not
• Not to be confused with extensions

[travisfont]

This is a huge enhancement and it's what separates the user from fully using Doogie over Chrome.