ENH: Simplify setup of ShapeVariationAnalyzerWidget

[jcfr]

This commit removes the explicit setting of ivars and instead uses
the function slicer.util.childWidgetVariables.

The updates was done following these steps:

1. Systematic replace of self.<widgetName> with self.ui.<widgetName>

script=ShapeVariationAnalyzer/ShapeVariationAnalyzer.py
for widget in $(cat $script | ack "getUI\('" | cut -d"'" -f2); do
  sed "s/self\.$widget/self.ui.$widget/" $script -i;
done

2. Manual removal of lines including self.getUI and removal of implementation of getUI function.

3. Additional replacements in script:

self.spinBox_colorModeParam1
-> self.ui.spinBox_colorModeParam_1

self.spinBox_colorModeParam2
-> self.ui.spinBox_colorModeParam_2

self.checkableComboBox_ChoiceOfGroup
-> self.ui.checkableComboBox_ChoiceOfGroup

self.collapsibleButton_creationCSVFile
-> self.ui.collapsibleButton_creationCSVFile

self.collapsibleButton_previewClassificationGroups
-> self.ui.collapsibleButton_previewClassificationGroups

self.collapsibleGroupBox_previewVTKFiles
-> self.ui.collapsibleGroupBox_previewVTKFiles

4. Additional replacements in UI file