Inconsistent use of MissingParameterException #102

java-client checks on the client side for missing parameters in MultiTouchAction::perform and throws a custom exception. However, there aren't other checks for valid params. We should check parameters consistently in the client or not at all.

Also, we should probably use Preconditions.checkArgument(foo, msg);, since this is part of the Guava idiom, and add throws IllegalArgumentException to function signatures that assert precondtions.