remember most recent tab (fixes #21)

Author: tckmn

src/main/java/mn.tck.semitone/MainActivity.java

@@ -80,13 +80,16 @@ public class MainActivity extends FragmentActivity {
 
         pager.setAdapter(adapter);
         tabs.setupWithViewPager(pager);
+        pager.setCurrentItem(sp.getInt("lastpage", 0));
 
         pager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
             @Override public void onPageScrollStateChanged(int state) {}
             @Override public void onPageScrolled(int pos, float off1, int off2) {}
             @Override public void onPageSelected(int pos) {
                 if (pos == 0) RecordEngine.resume();
                 else RecordEngine.pause();
+                e.putInt("lastpage", pos);
+                e.commit();
             }
         });