Create and hook up asynchronous database

Problem: Application performance is slow because of synchronous database calls that hog the browser thread, and large chunks of data are being held in browser memory.

As a user, I want a performant application that doesn't crash.

Acceptance Criteria

• Add PouchDB library to openlmis-ui-components

• Create "databaseService" which will wrap PouchDB create and delete methods, returning a reference to a pouchDB instance

• Add a listener to the openlmis-auth.logout event, that will delete all databases stored in the browser

NOTE: Discussion of local database selection is here