Add Google+ OAuth2.0.
Split items code out of icecrate.js

Now in icecrate-items.
Split households code out of icecrate.js

Now in icecrate-households.
Split shopping lists code out of icecrate.js

Now in icecrate-lists.
Split db sync code out of icecrate.js

Now in icecrate-sync.
Move filter `sumvals` into the only module that uses it.
Rename icecrate-db to icecrate-store.
Move server sync code from icecrate-store to icecrate-sync.