Refreshing on Bounty Creation loses all progress

**Steps To Reproduce**
Steps to reproduce the behavior:
1. Go to new bounty creation wizard
2. Complete a few steps, but dont submit work
3. Refresh page

**Observed behavior**
No warning that data will be lost

**Expected behavior**
Display an alert stating that data will be lost when he tries to refresh or leave the page, and offer them the option to cancel their action and retain data.

Start at the new bounty creation wizard and reproduce the listed steps to identify where its form state and page-leave behavior are handled. Add a warning when refreshing or leaving with incomplete work, allow cancellation to retain the data, and verify that the wizard state survives the cancelled action.

Written by the indexing model from the issue text.