cmake/modules/ECMAddAppIcon.cmake is heavily patched to support sidebar icons, OUTFILE_BASE parameter and to not include 64 and 64@2x icons on macOS which are not supported. All changes are made in a way that we can upstream this.
This implements out-of-repository-theming, and removes the old
custom.ini theming that never worked on all platforms and had
no straight deployment story.
The new approach requires the CMAKE variable OEM_THEME_DIR to
point to a directory that must at least contain an OEM.cmake file
(check OWNCLOUD.cmake for possible options) as well as a themes.qrc
and a themes/ directory that directly correspond to the ones in
the source tree.
