demodata vertical pressure levels contain wrong units

[Joern Ungermann]

The units are hPa, but for proper sideview plots they need to be Pa.

[Reimar Bauer]

Switched unit of air_pressure in demodata from hPa to Pa

Also expand horizontal extent of demodata at cost of time resolution for "nicer" plots. Adopted testcases accordingly

Fix issue #276

→ <<cset 567d4917a7b2>>