Bi-directional GitHub feature description updates

Currently the integration between Aha! and GitHub issues is uni-directional, Aha->GitHub. So if someone changes the initial post content in an integrated GitHub issue, the next time an update arrives from Aha! that change will be blown away.

Example of the impact: Often initial GitHub issue posts also include Markdown tasklists ("[ ]" or "[x]") for associated acceptance criteria or tasks. The underlying Markdown is changed to "[x]" as developers check things off in GitHub, but that data is blown away the next time Aha! syncs the Feature, effectively constantly resetting data about the progress of the issue.