Store config in JSON files
Development server

Add a small script to easily and quickly start a development server
Properly handle port numbers in URLs
Handle missing config.json better
Rename config key `url.hssdoc` → `url.hss`
Read both config.json and config.default.json
Improve the development server
Fix "Get started" popup close button

Close #450
Point "API docs" link to the new domain

Close #451
Fix manifesto images

Close #449
Fix indentation
Merge branch 'develop'