Investigate using more complex reducer with nested fields

[michalkvasnicak]

Basically store the whole form values state and use form reducer to dispatch actions over all fields, etc. Then just reflect the state of a field in local field state so we can easily read a field state without need to hack the state.

[michalkvasnicak]

Field state will be the same value as in form state for given field.
Changed could be tracked by incremental id of field state so we don't need expensive checks if something changed.