Update and unify the description of Games

This is also the description used on the website.

data/org.gnome.Games.appdata.xml.in

@@ -4,7 +4,7 @@
   <licence>CC0</licence>
   <project_license>GPL-3.0+</project_license>
   <_name>Games</_name>
-  <_summary>Simple game launcher for GNOME</_summary>
+  <_summary>Browse and play your games</_summary>
 
   <description>
     <_p>

data/org.gnome.Games.desktop.in

 [Desktop Entry]
 _Name=Games
-_GenericName=Video game player
-_Comment=View and play your video games collection
+_GenericName=Video Game Player
+_Comment=Browse and play your games
 _Keywords=game;videogame;video game;player;
 Exec=gnome-games %U
 Icon=org.gnome.Games

flatpak/gnome-games-nightly.flatpakref

 [Flatpak Ref]
 Title=Games (Nightly)
 Comment=Nightly version of GNOME Games
-Description=Games is a GNOME application to browse your video games library and to easily pick and play a game from it.
+Description=Browse and play your games
 Name=org.gnome.Games
 Branch=master
 Url=https://sdk.gnome.org/nightly/repo-apps/

gnome-games.doap

@@ -6,7 +6,7 @@
          xmlns="http://usefulinc.com/ns/doap#">
 
   <name xml:lang="en">Games</name>
-  <shortdesc xml:lang="en">Simple game launcher for GNOME</shortdesc>
+  <shortdesc xml:lang="en">Browse and play your games</shortdesc>
   <description xml:lang="en">
     Games is a GNOME 3 application to browse your video games library and to
     easily pick and play a game from it.