Add preference to set instant mix song number

app/src/main/res/values/arrays.xml

@@ -38,4 +38,16 @@
         <item>yes</item>
         <item>no</item>
     </string-array>
+
+    <string-array name="instant_mix_song_number_titles">
+        <item>10</item>
+        <item>25</item>
+        <item>50</item>
+    </string-array>
+
+    <string-array name="instant_mix_song_number_values">
+        <item>10</item>
+        <item>25</item>
+        <item>50</item>
+    </string-array>
 </resources>

app/src/main/res/values/strings.xml

@@ -13,6 +13,7 @@
     <string name="label_placeholder">--</string>
     <string name="label_dot_separator">•</string>
     <string name="save_filters">Save filters between sessions</string>
+    <string name="instant_mix_song_number">Number of songs generated by Instant Mix</string>
 
     <string name="sync_header">Synchronization</string>
     <string name="music_sync">Music sync</string>