Suppress warnings in generated Java source compilation units.

Author: benalexau

main/java/uk/co/real_logic/sbe/generation/java/JavaGenerator.java

@@ -1169,6 +1169,7 @@ else if (tokens.get(index).signal() == Signal.END_GROUP)
  private CharSequence generateClassDeclaration(final String className)
  {
  return String.format(
+ "@SuppressWarnings(\"all\")\n" +
  "public class %s\n" +
  "{\n",
  className