Fully initialise the PluginManager instead of passing around
one in various states of existance.
Move plugin extraction logic into a CorePluginExtractor class.
Inject UpdateManager where appropriate.
Change-Id: I6c15f7682cccd93b40dcc189a0a8466d067095f0
Reviewed-on: http://gerrit.dmdirc.com/2692
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager