Create view for empty drawing#index state

[steverabino]

What

Once #153 is merged, when new orgs/users are created, it is more likely that new users (of new orgs) will see a pretty empty app:

We should show a message to reassure user that it is empty only as no images have been uploaded yet, and a upload button (or instructions to use the existing upload button)

How

We could actually show a whole HowTo page when number of drawings shown is zero as we have the entire page to play with

Considerations

• Will need to co-exist with a solution for #144 as will usually be a "first-time user" thing

[krissy]

@CathMollie @rocioleon @EChesters @tanyapowell - thoughts? Important for first-time users. Any ideas on what to show in the meantime while a better UX solution is being confirmed?