getTreeViewCSS is unreadable on dark themes

[buckmelanoma]

getTreeViewCSS is used for the Files and Actions tabs and sets custom icons for the tree view elements. Since these are static images they remain black even when using a dark window color, making them nearly invisible.

Removing
m_tvTransaction->setStyleSheet(StrConstants::getTreeViewCSS());
and
m_tvPkgFileList->setStyleSheet(StrConstants::getTreeViewCSS());
from propertiestabwidget.cpp yields tree view elements that have proper contrast in dark themes:

[Alexandre Arnt]

Fixed in upstream.