Decrease model tests precision.
Merge pull request #259 from francisco-dlp/decrease_model_tests_precision

Decrease model tests precision.
Ignore Thumbs.db (windows meta-data file)
Fix ValueError on interactive signal range select

When selecting a range by the SpanSelectorInSpectrum, a ValueError is
raised initially when the left value is assigned, and the right value is
yet to be assigned (since the left can be higher than the right value).
Avoided by initing to NaN, and comparing on a ValueError.