server: support manual re-run of setup

**Is your feature request related to a problem? Please describe.**

When you add a session via the contender RPC server, create/setup steps happen automatically (in `Contender::initialize`). Some scenarios might want to re-run their setup steps, or deploy new contracts.

**Describe the solution you'd like**

Add two new endpoints to the RPC server:

- `deployContracts(session_id)`
- `runSetup(session_id)`

Each of these has a corresponding function in `TestScenario` (via `orchestrator::Contender::scenario`); call the respective functions.

Add buttons to the session pane in the webpage to trigger these RPC calls.