PTService should not be a SciJavaService

PTService has a significant number of sub-interfaces and subclasses, all
of which are directly extended by various services through the
SciJava software stack (e.g. in ImageJ2). Having PTService as a
SciJavaService thus causes all of these implementing classes to get
pulled into Contexts created with "SciJavaService.class" - which is
supposed to just provide the core services.

Subclasses should instead implement the correct scoping interface (e.g.
SCIFIOService or ImageJService).