CHANGE FEATURE: improve docs for new-plots in psyplot-gui

[Chilipp]

Summary

The plot creator widget has multiple not well documented features

Reason

At the moment, the table with the arrays, the coordinate combo boxes and the subplot creation is not documented

Current behaviour

Only plot method and formatoptions are documented, some widgets have tooltips

New behaviour

Some new docs should be implemented:

• [ ] general documentation/introduction to the widget should be created
• [ ] explain the columns in the array table
• [ ] subplot creation

Examples