Add example to databases and fixed splice bug emitting introns as variants

[jonas-fuchs]

• fixed bug which would lead to large variants being called for spliced features
• examples can be supplied with the database
• new example button in the webapp
• fixed how some tables are displayed
• fixed steps during showcase
• added better error message for mismatches during init
• adjusted plot text

[codecov]

Codecov Report

❌ Patch coverage is 90.60773% with 17 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
respro/core/vcf_remap.py	68.00%	5 Missing and 3 partials ⚠️
respro/db/cache.py	66.66%	3 Missing and 1 partial ⚠️
respro/core/alignment.py	94.91%	1 Missing and 2 partials ⚠️
respro/cli/init.py	90.47%	1 Missing and 1 partial ⚠️

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