add CheckBox widget to viewer.  fix ComboBox widget docstring
added tv_denoise.py viewer example using the CheckBox
fix image scaling in tv_denoise.py example
code formatting fixes
Remove blit background when overlay changes
Use functools.wraps in default_fallback dectorator
Merge pull request #1151 from blink1073/default_fallback_doc

Use functools.wraps in default_fallback decorator

Fixes #1149, allowing functions wrapped by `default_fallback` to keep their docstring.
Merge pull request #1146 from blink1073/master

Fix docstrings to be less confusing about pixel coordinates.
PEP8 formatting
Merge pull request #1150 from blink1073/overlay-blit

Remove blit background when overlay changes
remove outdated comment line
Merge pull request #1139 from grlee77/viewer_checkbox

Viewer: CheckBox Widget