That dependency for libgstreamer0 is for real old versions of opera. If you have an old version of opera installed, try uninstalling it and removeing any reference to opera sources in /etc/apt/sources.list.
If you successfully install a new version, it should add a new source to your /etc/apt/sources.list.
v47 installed ok on my machine. I installed with dpkg -i --simulate <packagename> to check for problems first.