cpp-130: Make drag buttons more usable

The maximum distance of detecting dragging was removed.
The minimum distance now uses DPI value.

Fixes #130

core/src/main/java/org/solovyev/android/calculator/CalculatorKeyboardImpl.java

@@ -44,7 +44,6 @@ public class CalculatorKeyboardImpl implements CalculatorKeyboard {
 
 	@Override
 	public void buttonPressed(@Nullable final String text) {
-
 		if (!Strings.isEmpty(text)) {
 			if (text == null) throw new AssertionError();