Added support for imports and many other .proto features.

Change-Id: I6600021b7ec8c486794349511232c3e604421c5b
Tested: on Linux.

tests/MyGame/Example/Test.java

@@ -7,6 +7,7 @@ import java.lang.*;
 import java.util.*;
 import com.google.flatbuffers.*;
 
+@SuppressWarnings("unused")
 public final class Test extends Struct {
   public Test __init(int _i, ByteBuffer _bb) { bb_pos = _i; bb = _bb; return this; }