[ux,dataset][s]: tweak sidebar layout (use icons more etc).
[tests][xs]: remove long obsolete test_catalog.py.
[tests][xs]: tiny bugfix to site tests.
[#28,tools][m]: refactor to move create dp.json code into tools and improve.

* split into 2 methods one for JTS and one for main dp.json
* improve in various (minor-ish) ways e.g. set format field, handle error cases better