Add time tracking bars and time to milestone issue cards
### Problem to solve
The overview of a milestone contains only the status of the milestone (doing or finished).
### Further details
More information about the milestone would be helpful to plan a project.
### Proposal
It would be useful to see more detailed information on one milestone at a glance to know more about the current state of the progress of one milestone. The table should contain all issues with the issue number, issue name, time estimate, time spent, the assignee, start and end date of the issue as well as the state (doing, closed, discarded).
(Discarded stands for issues that were planned, but then it was decided not to implement them. Therefore a special button should be added to the issue view, where it is possible to „Discard And close“ the issue. See related issue xx. In case this other issue is not/not yet implemented, the table will have one column less, hence the discarded column will be left out.)
The time estimate should be paired with a bar whose length is proportional to the time estimate of the issue.
If the time spent on an issue is higher than the time estimate, the number and the time units should be red.
At the bottom of the page the cumulated numbers for the milestone should be shown. These are the number and name of the milestone, the total hours estimated and spent for the milestone, the assignee, the start and due date, the number of open, doing and discarded issues. The suggestion is to accept only done issues in this percentage of done as the time spent might be higher than the time estimate. This is analogous to the (existing) overview of all milestones.
The page should also contain a table with the time estimate and spent of every assignee so that it is easy to get an overview of the milestone.

### What does success look like, and how can we measure that?
A table of detailed information about issue number, issue name, time estimate and time spent, the assignee, start and end date of the issue, as well as the state (doing, closed, discarded).
At the bottom of this table the cumulated numbers for the milestone should be shown.
A (second) table with the total hours of time estimated and spent by each assignee.
### Links / references
issue