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This is due a update to ejabbered where Nodes can now hold 10
items per default

Use absolute imports on all plugins

See merge request !43

This is necessary because Gajim is with 0.16.11 a python package

- Prepare the Plugin so it works with Gajim as a package.
- Add a Fallback method so we can update Plugins that are not loaded
by the PluginManager

This reverts commit 346da609

current Gajim version. Fixes #225

- Print only warning instead of error, as the module is only optional
- Log the error to the debug log, so users dont think we didnt catch the exception

The HTTPUploadPlugin calls that if encryption is enabled

Call the `encrypt_file` method of the encryption plugin instead