Disable tab switching in media overview during multiselect.

Multiselect only applies to items in the "media" tab, so people
shouldn't be able to switch tabs during multiselect.

src/org/thoughtcrime/securesms/components/ControllableViewPager.java

@@ -0,0 +1,32 @@
+package org.thoughtcrime.securesms.components;
+
+import android.content.Context;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
+import android.support.v4.view.ViewPager;
+import android.util.AttributeSet;
+import android.view.MotionEvent;
+
+/**
+ * An implementation of {@link ViewPager} that disables swiping when the view is disabled.
+ */
+public class ControllableViewPager extends ViewPager {
+
+  public ControllableViewPager(@NonNull Context context) {
+    super(context);
+  }
+
+  public ControllableViewPager(@NonNull Context context, @Nullable AttributeSet attrs) {
+    super(context, attrs);
+  }
+
+  @Override
+  public boolean onTouchEvent(MotionEvent ev) {
+    return isEnabled() && super.onTouchEvent(ev);
+  }
+
+  @Override
+  public boolean onInterceptTouchEvent(MotionEvent ev) {
+    return isEnabled() && super.onInterceptTouchEvent(ev);
+  }
+}