Add close all tabs button

app/src/main/java/org/kiwix/kiwixmobile/main/MainActivity.java

@@ -1079,6 +1079,13 @@ public class MainActivity extends BaseActivity implements WebViewCallback,
     return false;
   }
 
+  @OnClick(R.id.tab_switcher_close_all_tabs)
+  void closeAllTabs() {
+    webViewList.clear();
+    tabsAdapter.notifyDataSetChanged();
+    updateTabSwitcherIcon();
+  }
+
   @OnClick(R.id.bottom_toolbar_bookmark)
   public void toggleBookmark() {
     //Check maybe need refresh

app/src/main/res/layout/tab_switcher.xml

@@ -12,4 +12,16 @@
     android:layout_height="match_parent"
     android:orientation="horizontal"
     app:layoutManager="android.support.v7.widget.LinearLayoutManager" />
+
+  <android.support.design.widget.FloatingActionButton
+    android:id="@+id/tab_switcher_close_all_tabs"
+    android:layout_width="wrap_content"
+    android:layout_height="wrap_content"
+    android:layout_marginBottom="24dp"
+    android:contentDescription="@string/close_all_tabs"
+    app:backgroundTint="@android:color/black"
+    app:layout_constraintBottom_toBottomOf="parent"
+    app:layout_constraintEnd_toEndOf="parent"
+    app:layout_constraintStart_toStartOf="parent"
+    app:srcCompat="@drawable/ic_clear_white_24dp" />
 </android.support.constraint.ConstraintLayout>

app/src/main/res/values/strings.xml

@@ -239,4 +239,5 @@
   <string name="new_tab">New tab</string>
   <string name="switch_tabs">Switch tabs</string>
   <string name="smiling_face">:D</string>
+  <string name="close_all_tabs">Close all tabs</string>
 </resources>