#275: Separate apolloClient into module

[aswallace]

Separate apolloClient into its own module. Current version works with Vuex actions, but still requires cache and link (error below)
Note that omitting link and cache from new ApolloClient results in the following error:

In order to initialize Apollo Client, you must specify 'link' and 'cache' properties in the options object.
These options are part of the upgrade requirements when migrating from Apollo Client 1.x to Apollo Client 2.x.
For more information, please visit: https://www.apollographql.com/docs/tutorial/client.html#apollo-client-setup

close #275

[aswallace]

I tried this out on the spreadsheet upload branch, and it doesn't work with Vuex since the default export is a function that requires a parameter (so I can't do things like call apollo.mutate). Thoughts on how to fix it?

Edit: Resolved with recent changes

[tholulomo]

LGTM