Dialogy

- [x] feat: `DurationEntity` are cast as `TimeEntity` by default.
- [x] `DucklingPlugin` uses temporal intents to understand cast direction i.e. add duration to reference time or subtract.
- [x]: docs: Heavy addition of examples for types, plugins and base types.
- [x]: fix: Entity structures are uniform in terms of `value` and `values` attributes.
- [x]: feat: Guards prevent plugins from running.

- [x] fix: `entity.entity_type` and `entity.type` hold separate meaning.
- [x] update: Plugins no longer need `access` or `mutate` functions.
- [x] update: `Workflow` has `Input` and `Output` objects.

- [x] feat: plugin to merge previously tracked datetime entities with currently extracted datetime entities.
- [x] feat: New entity type credit-card / debit-card supported via `PlasticCurrencyEntity`.

- [x] feat: Sklearn based MLP classifier added as a plugin with gridsearch.

- [x] fix: XLM classifier wasn't using xlmrobert, but bert instead.

- [x] feat: ListSearchPlugin can find keyword entities via fuzzy search.