R.I.P. Cnchi — Calamares is now the primary installer

- Main install button now launches calamares-next instead of cnchi
  - Button label changed from 'Launch Cnchi Installer' to
    'Install Antergos NeXT'
  - Removed 'Alternative Installer' (Calamares) button — no longer
    needed since Calamares is the only installer
  - Welcome song path updated: /usr/share/cnchi-memes/ →
    /usr/share/antergos-next-memes/ (memes package repurposed)
  - Release notes page: added Cnchi retirement notice with eulogy
  - Readme page: updated instructions, removed cnchi-next link

ui/antergos-welcome.glade

@@ -369,7 +369,7 @@ We, the Antergos NeXT Developers, hope that you will enjoy using Antergos NeXT a
             <child>
               <object class="GtkButton" id="install">
                 <property name="visible">False</property>
-                <property name="label" translatable="yes">Launch Cnchi Installer</property>
+                <property name="label" translatable="yes">Install Antergos NeXT</property>
                 <property name="name">install</property>
                 <property name="can-focus">False</property>
                 <property name="receives-default">True</property>
@@ -433,20 +433,7 @@ We, the Antergos NeXT Developers, hope that you will enjoy using Antergos NeXT a
                   </packing>
                 </child>
                 <child>
-                  <object class="GtkButton" id="calamares">
-                    <property name="visible">False</property>
-                    <property name="label">Alternative Installer</property>
-                    <property name="name">calamares</property>
-                    <property name="can-focus">True</property>
-                    <property name="receives-default">True</property>
-                    <property name="tooltip-text" translatable="yes">Launch Calamares installer</property>
-                    <signal name="clicked" handler="on_action_clicked" swapped="yes"/>
-                  </object>
-                  <packing>
-                    <property name="expand">False</property>
-                    <property name="fill">True</property>
-                    <property name="position">2</property>
-                  </packing>
+    
                 </child>
               </object>
               <packing>