Do not show master password when using QFieldSync for the first time

Probably not the best way to solve it, but the easiest with no serious consequences.

If the user install QFieldSync and the default value of `qfieldCloudRememberMe=True`, it will call the `cloud_api.auto_login_attempt`, which calls the `QgsApplication.authManager()`.

As a UI this is asking for the master password, but the users have no idea what is this and what is the context of it. 

Fix #580

qfieldsync/core/preferences.py

@@ -31,7 +31,7 @@ def __init__(self):
         self.add_setting(Dictionary("qfieldCloudLastProjectFiles", Scope.Global, {}))
         self.add_setting(String("qfieldCloudServerUrl", Scope.Global, ""))
         self.add_setting(String("qfieldCloudAuthcfg", Scope.Global, ""))
-        self.add_setting(Bool("qfieldCloudRememberMe", Scope.Global, True))
+        self.add_setting(Bool("qfieldCloudRememberMe", Scope.Global, False))
         self.add_setting(
             String("cloudDirectory", Scope.Global, str(home.joinpath("QField/cloud")))
         )