Various fixes mainly relating to cropping

I made some changes in karthograph to make it work for my project, some of these are obvious, and some are a bit more risky, needs to be reviewed before integrating:
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map.py:
Padding is under opts['bounds']['data'] and not opts['bounds'] 
geometry/utils.py:
Removed always True from the min_area test
geometry/feature/Feature.py:
Make sure also the geometry you compare with is valid, and ignore errors
renderer/svg.py:
ignore some errors