Check in data-multipolygons.wkt

This file is created from others so doesn't have to be checked in,
but it makes it easier for users of the test repository.
Fix test:section tag in mp-tags tests
Add testcases for multipolygon tags.
Fix small bugs and typos in tests
New test.json file with metadata for each test.

This contains the contents of the description.txt, multipolygon.wkt, and
additionally the tags that are supposed to be on the created areas.
Add landuse=forest tag to area tests
More tests, test fixes, multipolygon sql now created from json
Remove multipolygons.wkt files (replaced by test.json)
Created test.json files for remaining tests
Remove description.txt files (now in test.json)