Add 'plotting input' tab

• can be found on analysis.sns.gov: /SNS/TOPAZ/IPTS-31189/shared/ReductionGUI/main.py
• can be run with mantidpython main.py
• Functions of this tab:
  • specify two files: FluxFile SAFile; optional, default value is None
  • specify some plotting parameters: axis (H K L), slicing location, thickness, range (xmin,xmax,...)
  • with the button click, generate config files under analysis.sns.gov:/SNS/TOPAZ/IPTS-xxxxx/shared/autoreduce/
• image at: https://code.ornl.gov/-/project/15050/uploads/45edc99233e734c7d11b52194bf2be66/plottinginputtab.png