refactor(tabs): change the material design tabs to act as bottom navigation

Update tabs to reflect the material design bottom navigation spec:
https://material.google.com/components/bottom-navigation.html#bottom-nav
igation-usage

BREAKING CHANGES:

Material design mode defaults have changed to the following:

```
tabsHighlight: false,
tabsPlacement: 'bottom',
tabsHideOnSubPages: false
```

`tabsHighlight` can now be passed as an attribute on the `ion-tabs`
element, this allows for tabs to be added in multiple places inside of
an app and enable the highlight on some of them.

references #7455

src/config/modes.ts

@@ -81,9 +81,9 @@ Config.setModeConfig('md', {
 
   spinner: 'crescent',
 
-  tabsHighlight: true,
-  tabsPlacement: 'top',
-  tabsHideOnSubPages: true,
+  tabsHighlight: false,
+  tabsPlacement: 'bottom',
+  tabsHideOnSubPages: false,
 
   toastEnter: 'toast-md-slide-in',
   toastLeave: 'toast-md-slide-out',