GUI: Improve DoubleSpinBox
- [x] Support scientific notation on input - [x] Display number in scientific notation where appropriate (#858) - [x] Don't display trailing zeros (#861) - [x] Increase step upon repeated action; reduce step upon change of direction - [x] Correct display of negative numbers ~~(broken in j.870a)~~ - [x] Respect limits given through DoubleProperty
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