Closes #125 #60 #178

The current UISliderWidget is limited due to the following factors:

• Instantiating a UISliderWidget requires a QLabel, which is updated to show the value of the slider
• The QLabel cannot be updated manually
• The slider does not support float/double values

This pull request originally removed the QLabel parameter in favour of a QDoubleSpinBox parameter. It was decided that to provide the best user experience and enable flexibility to modify the widget in the future, more changes would be required:

• The UISliderWidget class now inherits from the QWidget class, instead of QSlider
• The class now creates a QGridLayout, which ensures future flexibility in modifying/customising the arrangement of the subwidgets within the UISliderWidget
• Instead of a QDoubleSpinBox, a QLineEdit has been added so that users can fine-tune the widget's value
• New QLabels have been added to display the minimum, median and maximum values of the widget
• Validation (QValidator and conditional checks) has been added to ensure arguments and user inputs are valid, alongside behaviour to handle invalid inputs
• Parameterized unit tests have been added, testing the UISliderWidget specifically, see test_UISliderWidget.py
• Existing examples in the /examples/ folder have been updated to accommodate the updated UISliderWidget
• Docstrings have been added to the UISliderWidget class, the tests, and the example
• Calls to the UISliderWidget class have been updated elsewhere in eqt in line with the changes made

Current Tasks:

• Implement QLineEdit
• Remove hardcoded values
• Make sure spinbox is linked to slider
• Overload the init, one with the DSpinBox and one without
• Add min and max QLabels
• Consider whether to split the class into two separate classes
• Add tests for the widget to eqt