Update plugin code to use Java 5 language features

(Huge patch attached. Hopefully it can get reviewed/applied soon, before it becomes stale. Luckily the patch consists only of low-risk changes that shouldn't affect the logic functionality.)

Since the plugin now requires Java 5 anyways (MINVOKER-111), might as well update the code to take advantage of better language features.

• Removed all unavoidable "raw type" warnings.
• Where possible/equivalent, converted Iterator-based loops to enhanced for loops.
• Removed unnecessary dependencies to Iterator.
• Removed unnecessary casts.
• Enabled "useJava5" parameter of modello-maven-plugin.

These changes should make it easier to maintain the code later.