[Interactor] Support Image Data and Fix bugs

[hkchekc]

This Pull Request is based on PR #10 and further includes:

• Support for image data, including:
  • Use Rectangle instead of colored region for Tagged regions for Image
  • Change codes for supporting 3D data
  • If image, then no legends
• Add optional sliders for zooming on the y axis
• Change zooming sliders for both x and y axis from sliding on the absolute value to percentage scale because SliderWidget can only support values within 0-100 range
• Fix the unit checking problem that is mentioned in comments in PR #10
• PEP8 fixes
• Add docstrings and comments

[hkchekc]

finally!