create some constants for apps with special handling

app/src/main/kotlin/com/simplemobiletools/contacts/extensions/Activity.kt

@@ -63,9 +63,9 @@ fun SimpleActivity.startCall(contact: Contact) {
 fun SimpleActivity.showContactSourcePicker(currentSource: String, callback: (newSource: String) -> Unit) {
     ContactsHelper(this).getContactSources {
         val ignoredTypes = arrayListOf(
-                "org.thoughtcrime.securesms",   // Signal
-                "org.telegram.messenger",       // Telegram
-                "com.whatsapp"                  // WhatsApp
+                SIGNAL_PACKAGE,
+                TELEGRAM_PACKAGE,
+                WHATSAPP_PACKAGE
         )
 
         val items = ArrayList<RadioItem>()

app/src/main/kotlin/com/simplemobiletools/contacts/helpers/Constants.kt

@@ -113,3 +113,8 @@ val localAccountTypes = arrayListOf("vnd.sec.contact.phone",
         "com.android.huawei.phone",
         "Local Phone Account"
 )
+
+// apps with special handling
+const val TELEGRAM_PACKAGE = "org.telegram.messenger"
+const val SIGNAL_PACKAGE = "org.thoughtcrime.securesms"
+const val WHATSAPP_PACKAGE = "com.whatsapp"