Added preferences.txt option to disable preferences save

Fix #5668

Author: cmaglie

arduino-core/src/processing/app/PreferencesData.java

@@ -114,6 +114,9 @@ static protected void save() {
     if (!doSave)
       return;
 
+    if (getBoolean("preferences.readonly"))
+      return;
+
     // on startup, don't worry about it
     // this is trying to update the prefs for who is open
     // before Preferences.init() has been called.

build/shared/lib/preferences.txt

@@ -279,6 +279,9 @@ serial.line_ending=1
 # default chosen language (none for none)
 editor.languages.current = 
 
+# Disable saving of preferences.txt file (settings will not survive Arduino IDE reboot)
+preferences.readonly=false
+
 # Debugging/Development Preferences
 # ---------------------------------