[WIP]Add filter interface to any filterable resource view

Currently, the only way to add filters to resource view is when they're inside a `ckanext-dashboard`. Ideally, we could add these filters anywhere a filterable resource view is displayed.
If a filter value is the string representation of a number, `queryStringToJSON` will cast it to a number - and the call to `split('|')` will fail. (I know numerical filters aren't supported yet - but this can happen if you have field which contains a mix of text and numbers - I have seen this problem in practice.).

It would be safer to do:
```javascript
fieldValuesStr = String(searchParams.filters).split('|');
```