Make end date of board membership more explicit on board page

One-sentence description

On a board page of a board where board members changed roles of terminated the board early, that is unclear.

Current behaviour / Reproducing the bug

Check for example the page of board 17-18. Currently the roles are indicated in the role name ("chair until xxxxxxxx"). Of course you would want it as just "chair" since it otherwise is also weird for achievements.

Expected behaviour

In case people switched roles or quit early: show all roles including dates, or only the most recent one including dates. If a person quit the board early, it could also be greyed out possibly.