Catanzaro: GNOME 3.22 core apps

Michael Catanzaro laysdown the rules for which GNOME applications distributions should package ifthey want to claim to provide a "pure GNOME experience." "Selectingthe right set of default applications is critical to achieving a qualityuser experience. Installing redundant or overly technical applications bydefault can leave users confused and frustrated with thedistribution. Historically, distributions have selected wildly differentsets of default applications. There's nothing inherently wrong with this,but it's clear that some distributions have done a much better job of thisthan others."