Fix Warnings on Launch

[shun-iwasawa]

This PR will refactor sources and resource images in order to resolve all warnings appears on launching the software with console.

Here is a list of resolved warnings:

QMetaObject::indexOfSignal: signal updateVisibility() from CommandBar redefined

Removed signal updateVisibility() from XSheetToolbar class definition as it is already defined in the base class CommandBar. Also removed bool m_isCollapsible; variable for the same reason.

in XsheetGUI::XSheetToolbar
QWidget::setMinimumSize: (XSheetToolbar/XsheetGUI::XSheetToolbar) Negative sizes (-5,30) are not possible

Made XsheetViewer::positionSections() to be executed only if the Xsheet panel is visible, since this function seems to be needed to be called only from showEvent and resizeEvent.

QLayout: Attempting to add QLayout "" to StyleEditor "", which already has a layout

Made a new private function StyleEditor::createVectorPage() in order to make the ctor of StyleEditor cleaner. Made the sub-layouts to be constructed without parent widget pointer in order to avoid resetting of the parent widget.

PaletteViewerGUI::PaletteTabBar(0xc6d6d50, name="PaletteTabBar") does not have a property named "BottomAboveLineColor"
DVGui::TabBar(0xc51b240, name="StyleEditorTabBar") does not have a property named "BottomAboveLineColor"

Removed &:extend(.tab-container all); from claimed objects in style sheets as they are not used.

libpng warning: iCCP: known incorrect sRGB profile

Applied lossless file optimization to all resource PNG images in order to remove sRGB information (which may be added by PhotoShop). I used FileOptimizer by Javier Gutiérrez Chamorro. It could reduce the file size as well. 👍
Please note that the second commit ( optimize png files ) in this PR is dedicated to this.

[shun-iwasawa]

Jenkins

[shun-iwasawa]

Jenkins again

[masafumi-inoue]

LGTM