Created attachment 97886 [details] terminal output As in description. Look at attachment, please. The problem is that oxygen5-icon-theme has weird dependencies. I carelessly uninstalled it and it uninstalled Okular and I can't install Okular now because of the bug with processing oxygen5-icon-theme KDE Neon on Kubuntu 15.10 unstable, Plasma 5.6.90
The error on the attached log indicates that both the oxygen5-icon-theme and libkdepim5 plugins are providing: /usr/share/icons/oxygen/256x256/mimetypes/x-mail-distribution-list.png This is seen on my (neon) machine as well.
oxygen-icon-theme now replaces/breaks old libkdepim5 We don't have a build of kdepim which is compatible with this version of oxygen-icons yet. This means it'll be held back if you have kdepim installed. You can force it to be installed with apt install oxygen5-icon-theme which will uninstall kdepim