Fetch changelog from GH or atomicexplorer.com using API

[himu007]

Currently Agama uses hardcoded changelog for in-app display. Would be nice if Agama would fetch the changelog from online from github or atomicexplorer.com

In this case, we can update changelog with required changes anytime and Agama can fetch latest always.

[sawlysawly]

then this does mean that old agama versions will displays new changelog

might be confusion if users is on old version and they saw the changelog showing the new version