Upgrade bundled WhisperBack package to 1.5~rc1

The Changelog reads:

New features
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 * UI: guide the user if an error occurs while sending the bugreport.
   Propose to send it after 2 faild attempts.

Minor improvements
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 * Follow good coding standards thanks to pylint
 * Update Tails URL and email address.

Bugfixes
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 * Catch encryption exceptions in the right order
 * Remove duplicated function cb_close_application