User discussion threads / feedback

[mdoering]

Develop a generic user discussion system that works similar to github issues. Within a comment it should be possible to crosslink users (@mdoering), names (#Abies_alba) and other discussions (#63).

Threads should probably be scoped to a given dataset in the Clearinghouse and default to the CoL and its extended version.

Develop name pages that exist for every name (in CoL?), tracking all data changes and any user comment from issue threads that mention a given name.

Provide a user dashboard that shows the latest notifications and a system wide summary for the latest activities.