Reorganize view

View/ directory are reorganized into:

• db_config/ : for all gui to view/edit db table
• plotting/ : for all plotting dialogs/widgets

plotting_widget.py are split into different files under directory plotting/plotting_widget

• plotting_axes.PlottingAxes : figure and axes methods
• plotting.Plotting : inherit PlottingAxes and includes plotting channel methods
• plotting_widget.PlottingWidget: inherit Plotting and includes methods to handle different events