slackbuilds_ponce/network/Quaternion

Quaternion is a cross-platform desktop IM client for the Matrix
protocol.

SlackBuild notes:

* -DUSE_KEYCHAIN=0 is set - I was not able to get Quaternion to use the
  version of qtkeychain from slackbuilds.org. YMMV.

* -DUSE_INTREE_LIBQMC=0 is set to use the system copy of libQuotient.
  Using the in-tree version requires the sources to be fetched
  recursively via git, since it's a submodule. You probably don't want
  to change this.