Added connection debug mode

Created by: brlumen

One of the users of the plugin could not figure out the setting. The plugin constantly reported "Telegram returned an invalid response!". I added the ability to debug the connection in the functionality of the plugin. Also, the logic of checking the installation of the hook and the list of associated users was taken to a separate page "Users monitor" to avoid a situation in which it is impossible to disable debugging because the file might not be available for recording.

Also, the situation was eliminated in which php issued a warning about a non-initialized variable.