Add parameter / token support for simple search

Description: Parameterise static query to support variable / dynamic search options

Key decision at this iteration is where the front v back end split falls.

Breakdown: Incorporate core relative query parameters (tokens): current user, current date

• Preconfigure query for {currentuser}
• Query relative to today
• Parse date variables in different date contexts
• Lookup external token options for parameterised fields (eg, user)

Development Tasks:

1. Define token shape for dates
2. Work out whether this needs to be defined/fetched from the backend on a per type basis, or storage in frontend per type is sufficient.
3. Tie this to field type, eg String vs Id, String vs Date, to enable the frontend to dynamically offer tokens on relevant fields only.