Concentrate SharedPreference usage in a single class

Also add missing senderIds save.
Fix LTR warning
Fix PendingIntent mixing

PendingIntent are deduplicated using Intent.filterEquals(),
and extra keys are not considered in the process.

This caused the last notification to be shown even if the user clicks on
an older one.
Automatic initialization
Timely send notification received in more circumstances
Refresh the push token after each package upgrade