"Unmet dependencies" When trying to install KDE Plasma 5.3 on Ubuntu 15.04

Fixed it by:

sudo dpkg -P unity-scope-gdrive account-plugin-google account-plugin-facebook
sudo apt-get install -f

This removes the packages listed in the first command and thus resolves the package conflict.

By default, the package manager refuses to overwrite files that also appear in other installed packages (whether the file is actually there or not), which is a sane decision to not inadvertently corrupt packages. In your case, this means, that the packages are incompatible. I can see that one seems to come from a PPA, so you should write to the maintainer of that PPA to investigate the issue.

Meanwhile, since the conflicting file is only and icon, it's pretty safe to override the package manager's decision with --force-overwrite:

cd /tmp
apt-get download kde-config-telepathy-accounts
sudo dpkg -i --force-overwrite kde-config-telepathy-accounts_*.deb
sudo apt-get install -f

I solved with the following:

1. Find the deb that is causing the problems:

   sudo find /var/cache -name "kde-config-telepathy-accounts*"
   

   In my case the package was at

   /var/cache/apt/archives/kde-config-telepathy-accounts_4%3a15.12.3-0ubuntu1_amd64.deb
   

2. Install it with --force-overwrite:

   sudo dpkg -i --force-overwrite /var/cache/apt/archives/kde-config-telepathy-accounts_4%3a15.12.3-0ubuntu1_amd64.deb
   

   The command will complete with errors anyway

3. Fix the installation

   sudo apt-get -f install