Fix Milestone collapsed sidebar, adjust some aspects of issue sidebar

What does this MR do and why?

Collapsed milestone sidebar

• Fix broken milestone progress bar
• Fix start and end date widget height
• fix issue icon
• fix MR icon

Issuable collapsed sidebar

• Change "No iteration" to "None"
• Change "No epic" to "None"
• Change "No milestone" to "None"

Time spend widget collapsed state

• Change font size and weight to match other collapsed state widgets

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Page	Before	After
Milestone page
Issue page

How to set up and validate locally

1. Check out this branch
2. Visit a milestone page
3. Add start and end dates
4. Add some time spent to an issue in the Milestone
5. Collapse the sidebar if it isn't already
6. You will see in the sidebar that the progress bar appears, the start and end dates widget is not cut off, and the time spent widget text is not bold and is the same size as the other text. You will also see that the Issues icon matches the issues icon used in the Issues tab of the page.
7. Visit an issue
8. Collapse the sidebar if it isn't collapsed already
9. You will see that the time spend widget matches the style you saw in the Milestone page
10. Make sure there is no epic, no iteration and no milestone; each widget will say "None" instead of "No $THING"