Added tests for keyPressEvent() methods & fixes

[FillBk]

Tested shortcuts from classes:

• in file.py
• FileWidget
• in main.py
• MainWindow
• in numeric.py
• TableView
• Numeric
• in plot.py
• Plot
• PlotGraphics
• in tabular_base.py
• DataTableView
• TabularBase
• DataFrameViewer
• in tree.py
• TreeWidget
• Channels_Tree_Widget

Drag and Drop issue status:

• resolved

Added shortcuts:

• Ctrl+X -> Cut a channel or channels from ChannelsTreeWidget

Fixes:

• test/asammdf/gui/dialogs/test_FunctionsManagerDialog.py
• move test files in related folders
• added methods for better set up and evaluation processes
• restructure git strategy matrix (windows first)
• added a method to save a screenshot of widget as artefact for debugging