Fix windows build
Summary:
We need to export symbols when building the library, but import them
when using the library.
Fixes issues like:
.../moc_nicknamewidget.cpp(65): error C2491: 'ContactEditor::NicknameWidget::staticMetaObject': definition of dllimport static data member not allowed
Reviewers: sengels, mlaurent, dvratil
Reviewed By: dvratil
Subscribers: dvratil, kde-pim
Tags: KDE PIM
Differential Revision: https://phabricator.kde.org/D18523