Contract Tool: build out MVP based on current designs and current api

Implement the UI for the Contracts module.

## Resources

* [Schema](https://docs.greenstand.org/admin-panel/contract-system/domain-model-and-dictionary)
* [Domain dictionary](https://docs.google.com/document/d/1rXM24AXr5nhN8HHfbdavJa08JNF6RIVdPJp103jzEVU/edit?usp=sharing)
* [Column attributes](https://docs.google.com/document/d/1Z-BzykHM4iw8LwRxEolwJOChYhL2Lxk8LZOsceeKp-0/edit?usp=sharing)

## MVP scope

### In scope:
* Creation and management of Contracts (contract) including Contract Status (contract_status_enum)
* Attaching Documents (document) to Contracts (via contract_document)
* One fixed, generic Agreement (agreement) that can be applied to multiple Contracts
* Capture <-> Contract linkage (treetracker.capture.contract_id)
* Earnings <-> Contract linkage (earnings.earnings.contract_id)

### Not in scope:
* Agreement management UI
* contract_region
* species_agreement
* species_payout
* coordination_team
* coordinator
* consolidation_rule

## API
The schema is implemented in https://github.com/Greenstand/treetracker-contract-api and deployed at https://dev-k8s.treetracker.org/contract/.

## Design assets
* [Contracts tool design (Figma)](https://www.figma.com/file/G4Kl9fzLRgnk0SaeTne1Mc/Admin-Panel---Master?node-id=7575%3A5441&t=p5oPQjMiSubmuqv2-1)
* [Contracts tool workflows](https://www.figma.com/file/q8RmrvSg0ZfNirxHKBFG49/Greenstand---Admin-Panel---Contracts---User-Flows?node-id=0%3A1)