KPluginLoader move

[Alex Merry]

Just a heads up that I'm planning to move KPluginLoader, KPluginFactory
and kexportplugin.h from KService to KCoreAddons this weekend, as
previously discussed (it's SC, as it will involve putting KCoreAddons
into the link interface of KService).

I have an open review request for KPluginLoader in KService, but I'll
just discard it and re-open it in KCoreAddons.

Alex