Make status 'popup' button more appopriate size on OSX

Summary:
Due to small size, button Requires 'Qt::WA_MacMiniSize' attribute.
In addition, 'm_pButton->setMaximumHeight( maximumHeight );' caused problems.

Test Plan: Test on varity of platforms, verify popup button is as expected

Reviewers: kfunk

Reviewed By: kfunk

Subscribers: kfunk, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D657