refactor(lookandfeelexplorer): Port almost entire look and feel explorer to QQC2

Test Plan:
{F7822910}
{F7801659}

Reviewers: #vdg, #plasma, davidedmundson

Reviewed By: #plasma, davidedmundson

Subscribers: davidedmundson, GB_2, filipf, guoyunhe, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D25778