Wg 45 loading screen prevent navigation while data loading

[chrismcanulty]

1. Create loading screen to render while workout data is retrieved from API
2. Create dummy component to render in case there are no favourites yet (have confirmed this renders when all workout tokens have been removed from async storage, pretty straight forward so have not done so again for screenshot backup)
3. Create KeyboardAvoidingView for num pad/keyboard user inputs
4. Restyle favourite workout list - now not able to see buttons behind 'home' button and styles are differentiated from 'home' button as well

JIRA ticket: https://lhl-midterm-ecommerce.atlassian.net/browse/WG-45

Screenshots:

Loading screen

Restyled modal and added KeyboardAvoidingView

Restyle favourite workout list