Change "tabs" to "bottomTabs" (#1314)

* Change "tabs" to "bottomTabs"

* Fix failing test

lib/src/commands/LayoutTreeParser.js

     if (simpleJsonApi.sideMenu) {
       return this._createSideMenu(simpleJsonApi);
     }
-    if (simpleJsonApi.tabs) {
-      return this._createTabs(simpleJsonApi.tabs);
+    if (simpleJsonApi.bottomTabs) {
+      return this._createTabs(simpleJsonApi.bottomTabs);
     }
     return this._createContainerStackWithContainerData(simpleJsonApi.container);
   }
     children.push({
       type: LayoutTypes.SideMenuCenter,
       children: [
-        layout.tabs ? this._createTabs(layout.tabs) : this._createContainerStackWithContainerData(layout.container)
+        layout.bottomTabs ? this._createTabs(layout.bottomTabs) : this._createContainerStackWithContainerData(layout.container)
       ]
     });
     if (layout.sideMenu.right) {

lib/src/commands/LayoutTreeParser.test.js

         });
     });
 
-    it('parses tabs with side menus', () => {
+    it('parses bottomTabs with side menus', () => {
       expect(uut.parseFromSimpleJSON(SimpleLayouts.tabBasedWithBothSideMenus))
         .toEqual({
           type: 'SideMenuRoot',

lib/src/commands/SimpleLayouts.js

 };
 
 export const tabBasedApp = {
-  tabs: [
+  bottomTabs: [
     {
       container: {
         name: 'com.example.ATab'
 };
 
 export const tabBasedWithBothSideMenus = {
-  tabs: [
+  bottomTabs: [
     {
       container: {
         name: 'com.example.FirstTab'

playground/src/containers/WelcomeScreen.js

 
   onClickSwitchToTabs() {
     Navigation.setRoot({
-      tabs: [
+      bottomTabs: [
         {
           container: {
             name: 'navigation.playground.TextScreen',
 
   onClickSwitchToSideMenus() {
     Navigation.setRoot({
-      tabs: [
+      bottomTabs: [
         {
           container: {
             name: 'navigation.playground.TextScreen',