Add sliders for parameters

[StephenNneji]

Create a Slider widget, the widget should be laid out similar to the mock below.

1. This should be accessible via the menu Tools > Show Slider. When the show slider menu is clicked the project widget should be replaced with slider widget
2. The widget should have the following behaviour
   • The slider widget should populate with all fitted parameters and experimental parameters i.e. the one that are checked .
   • Each slider can be moved between the minimum and maximum values of the parameter.
   • Similar to RasCAL 1, dragging and releasing the slider should update the plot.
   • Clicking the Accept Changes button should update project but clicking the Cancel button will revert changes.
3. Add simple test for the Slider widget