Remove Mozilla branding

This merge requests removes most public 'Mozilla' and 'Firefox' branding and renames the application from 'Firefox Send' to 'Send'.

This is useful to allow to legally self-host Send, as 'Mozilla' and 'Firefox' are trademarks.

Dockerfile

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-# Firefox Send - Mozilla
+# Send
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-# License https://github.com/mozilla/send/blob/master/LICENSE
+# License https://gitlab.com/timvisee/send/blob/master/LICENSE
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