[WIP] Shortcuts tests development branch

[FillBk]

Unittests for shortcuts:

file	class	actual status
main.py	MainWindow	[ ]
file.py	FileWidget	[x]
list.py	ListWidget MinimalListWidget	[ ] [ ]
numeric.py	TableView Numeric	[x] [x]
plot.py	Plot PlotGraphics	[x] [x]
signal_scale.py	ScaleDialog	[ ]
tabular_base.py	DataTableView TabularBase DataFrameViewer	[ ] [ ] [ ]
tree.py	TreeWidget ChannelsTreeWidgets	[x] [x]

• ▢ = Unfinished
• 🗹 = Finished