Home page - add floating action button

[niall-rb]

Description
We want the user to be able to add events. This will be done through clicking on a floating plus icon on the home page. This should bring up a modal where eventually we'll allow a user to add an event.

This ticket is just for creating the icon that will bring up the modal, not the event creation process itself. While arguably doesn't deliver end to end value, it is important for giving the home page the correct look and feel before developing other parts of the app.

Out of scope
The actual event creation process.

Acceptance criteria
GIVEN A user navigates to the home page
WHEN The interest filter is not active
THEN They should see a floating action button

GIVEN A user navigates to the home page
WHEN When the user clicks on the floating action button
THEN They should see a blank modal

Non-functional requirements
The design should match those provided in Badger Me App

Linked issues
Android - FAB - Create Event