Support custom font in the Menu items. (#1030)

* Support custom font in the Menu items.

* Fix check for custom font.

android/app/src/main/java/com/reactnativenavigation/utils/TypefaceSpan.java

+package com.reactnativenavigation.utils;
+
+import android.graphics.Paint;
+import android.graphics.Typeface;
+import android.text.TextPaint;
+import android.text.style.MetricAffectingSpan;
+
+public class TypefaceSpan extends MetricAffectingSpan {
+    private Typeface mTypeface;
+
+    public TypefaceSpan(Typeface typeface) {
+        mTypeface = typeface;
+    }
+
+    @Override
+    public void updateMeasureState(TextPaint p) {
+        p.setTypeface(mTypeface);
+        p.setFlags(p.getFlags() | Paint.SUBPIXEL_TEXT_FLAG);
+    }
+
+    @Override
+    public void updateDrawState(TextPaint tp) {
+        tp.setTypeface(mTypeface);
+        tp.setFlags(tp.getFlags() | Paint.SUBPIXEL_TEXT_FLAG);
+    }
+}

android/app/src/main/java/com/reactnativenavigation/views/TitleBarButton.java

 
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
+import android.text.SpannableStringBuilder;
 import android.view.Menu;
 import android.view.MenuItem;
 import android.view.View;
 
 import com.reactnativenavigation.NavigationApplication;
 import com.reactnativenavigation.params.TitleBarButtonParams;
+import com.reactnativenavigation.utils.TypefaceSpan;
 import com.reactnativenavigation.utils.ViewUtils;
 
 import java.util.ArrayList;
     }
 
     MenuItem addToMenu(int index) {
-        MenuItem item = menu.add(Menu.NONE, Menu.NONE, index, buttonParams.label);
+        MenuItem item = createMenuItem(index);
         item.setShowAsAction(buttonParams.showAsAction.action);
         item.setEnabled(buttonParams.enabled);
         setIcon(item);
         return item;
     }
 
+    private MenuItem createMenuItem(int index) {
+        if (!buttonParams.font.hasFont()) {
+            return menu.add(Menu.NONE, Menu.NONE, index, buttonParams.label);
+        }
+        TypefaceSpan span = new TypefaceSpan(buttonParams.font.get());
+        SpannableStringBuilder title = new SpannableStringBuilder(buttonParams.label);
+        title.setSpan(span, 0, title.length(), 0);
+        return menu.add(Menu.NONE, Menu.NONE, index, title);
+    }
+
     private void setIcon(MenuItem item) {
         if (hasIcon()) {
             item.setIcon(buttonParams.icon);
     }
 
     private void setFont() {
-        if (buttonParams.font == null) {
+        if (!buttonParams.font.hasFont()) {
             return;
         }
         ArrayList<View> buttons = findActualTextViewInMenuByLabel();