Improve Compiler plugin implementation

[astares]

Strange hierarchy:

• at the moment we have OCCompilerASTPlugin saying it is "I am an abtract superclass for compiler plugins." in the class comment
• but the "dynamic" (block closure based) compiler plugins like OCCompilerDynamicASTPlugin are not implemented as a subclass - (they inherit from Object directly)
• also 'OCCompilerASTPlugin isAbstract ' returns false at the moment
• additionally: not all the methods in OCCompilerASTPlugin are required for a plugin - only #transformation: and #priority methods define the API called from the compiler side

=> We should cleanup and unify into the following hierarchy

• OCCompilerPlugin (abstract)
  -- OCDynamicCompilerPlugin
  -- OCStaticCompilerPlugin
  --- FFICompilerPlugin
  --- ASTPluginMeaningOfLife

Other code problems we should directly fix:

• also OCCompilerASTPPlugin has a class side subclassResponsibility for #priority which is fulfilled by both subclasses (ASTPluginMeaningOfLife and FFICompilerPlugin) - but it still returns a hard coded instance side #priority of 100
• #transform is categorized/classified as API - but it is not public API (its called privately)
• fix typo in ASTPluginMeaningOfLife>>#transform
• the plugin classes should be in a class category 'Plugins' similar to how their tests were tagged