Issue Boards sidebar async loading
Currently, all information of a given board issue is loaded when entering a Board, including the data needed for the Sidebar, which (probably) most of the time is not even accessed by the user.
Ultimately we should be loading the Sidebar information only when needed (i.e. async loading when clicking on a Board Issue). A similar behavior can be found on 'Issue' and 'Merge Request' main pages.
Edited by Oswaldo Ferreira