Support adding stores to a specific DB [Missing feature]

[galangel]

We found that the create store method does not support modifying existing DB,
we want to be able to append stores in the same DB, using the createStore function we would like to add a specific store to a DB but currently, it just returns the store object and does not actually submit changes in the DB

We belive the issue occurs because the idb-keyval does not support versions (changes) when using the createStore.