Add support to customize footer text in Paginator

[Andre601]

Issue

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Description

I would like it, if a method could be added to customize/alter the footer, including to set an avatar, the text displayed (Maybe add the "Page n/n" after the provided one?) and a timestamp.

That way could the paginator stick to the design that the bot may use through different commands. (e.g. showing a Requested by: <user> text in the footer)

[Sheldan]

This would be a welcome change, because I realized that the "Page" in the footer text is hardcoded, which would relate to #54 as well. So a possibility to customize this, would be included in this feature request.