Removed the annotation configuration code from DocumentMonitor

The processed and processing annotations are now declared and configured in
the plug-in manifest
Don't use the earlyStartup mechanism to initialise the document monitor
Added a new base trait for classes encapsulating Coq commands
Deleted almost all of the CoqJavaProject class

In future, JavaEditorState will replace this class entirely. For now,
though, a few vestiges of it survive to keep the rest of the code happy
Don't maintain a mapping between IDocuments and CoqJavaProjects

JavaPosition.getProj now unconditionally returns null
Handle the properties associated with AST nodes in a safer manner

The actual property names (for three of the properties, at least) are now
hidden away behind setters and getters
Added highlighting support to the Java proof mode

This is still just a prototype -- automatic retraction isn't supported yet