Remove dependency on okularpart from the mobile components
Summary:
This only depended on okularpart due to the export header used in the
kcfgc file, so use a dedicated one for the mobile components that doesn't
export anything.
This enables disabling the part build for mobile-only builds such as
Android, and thus removing the need for some difficult dependencies
like KParts.
Reviewers: aacid
Reviewed By: aacid
Subscribers: aacid, okular-devel
Tags: Okular
Differential Revision: https://phabricator.kde.org/D19037