EXP_DEMO_H5 from API

[emanuel-schmid]

Changes proposed in this PR:

• use climada data api to get the EXP_DEMO_H5 file in tests
• the one from the demo data directory has pickled shapely data that will not be readable soon
• the file is 1.1M in size so replacing it is not really an option

This PR fixes #1236 (at least partially)

PR Author Checklist

• Read the Contribution Guide
• Correct target branch selected (if unsure, select develop)
• Descriptive pull request title added
• Source branch up-to-date with target branch
• Documentation updated
• Tests updated
• Tests passing
• No new linter issues
• Changelog updated

PR Reviewer Checklist

• Read the Contribution Guide
• CLIMADA Reviewer Checklist passed
• Tests passing
• No new linter issues

[chahank]

Looks good to me. Thanks!