[renderjs_ui] Refactor FloatField and fix HTML5 Input
FloatField
- Put back default minimal step necessary for field validation
- Remove field_json.value because that one is never send by ERP5 backend
- Set comprehensive initial state and avoid sneaking state variables afterwards
- Handle better NaNs which represent empty numerical value
- Refactor for shorter and simpler code
- Rename "percents" -> "percentage" according to coding style guidelines
HTML5 input is not naive about missing values