Center about icons and code optimizations

[Donnnno]

Found some suggestions while going through the project in Android Studio:

Fixed

• Social icons are always centered
• OnBackPressedCallback > OnBackPressedCallback
• 'drawable.length() == 0' can be replaced with 'drawable.isEmpty()'
• Statement lambda can be replaced with expression lambda
• Explicit type argument String, Object can be replaced with <>
• 'isConnected()' is deprecated

Found some other interesting things that might be worth looking at:

• It will always be more efficient to use more specific change events if you can. Rely on notifyDataSetChanged as a last resort.
• 'enablePendingPurchases()' is deprecated
• getIdentifier is discouraged:
  Use of this function is discouraged because resource reflection makes it harder to perform build optimizations and compile-time verification of code. It is much more efficient to retrieve resources by identifier (e.g. R.foo.bar) than by name (e.g. getIdentifier("bar", "foo", null)).