Add constant components in top-level component

Idea:

To make a united layout throughout the app.

1. Include top-level components like navbar, constant images like logos in a top-level component such as Layout.js. Remove them from DiagnosticContainer component
2. Use Material-UI theming
3. As per @friedger and @AdhamAH suggestions, keep constant components in Layout.js’ and React providers in ‘App.js’

Motivation:

1. Keep consistency in the styling of the app
2. Make it easier for anyone new coming on board to follow the same flow
3. Start implementing Material-UI

[friedger]

I think it is good practise to put all the react providers in App.js and the constant components into something like Layout.js, then the components for all routes can make use of Layout as top level component.

[SomeMoosery]

I think anything top-level like this could go within App.js, unless that’s bad practice, not too sure.

I was thinking DiagnosticContainer would be the wrapper component for the Health Log, containing both the overview and also weekly view. I don’t know if we should repurpose this.