Add support for increment/decrement and array operations

[clintharris]

Currently only "set" is supported.

• There's no good way to do this without deviating from the IndexedDB API (which really only supports "set" ops)
• It would involve modifying the oplog entry objects to specify the type of operation (set/increment/insert). Example:

  {
    hlcTime: '2021-01-24T13:23:14.203Z-0002-testnode',
    store: TODO_ITEMS_STORE,
    objectKey: defaultTodo.id,
    operation: 'increment' // 'decrement' | 'set' | 'arrayInsertAtIndex' | 'arraySetAtIndex' | 'arrayRemoveAtIndex', etc.
    prop: 'someCounter',
    value: -1
  }
  

• Note that supporting array operations (i.e., insert, mutate at index, etc.) is not a pre-requisite. A feasible (and possibly simpler) solution is to normalize objects. Instead of { id: 1, things: [thing1, thing 2] }, create a separate object collection for things and associate them with the parent object.