Milestone link missing HTML escaping (BB-10395)

The milestone link in comments in issues isn't escaped properly. This causes the URL of a milestone to be invalid (non-working) if certain characters are used that should be url-encoded when using as a parameter.

Steps to reproduce:

1. Create a milestone with the name "milestone; bug"
2. Create issue, not linking to the milestone yet
3. Edit the issue and set the milestone to "milestone; bug"
4. A new comment will appear like "changed milestone to milestone; bug"
5. Look at the URL insert in this comment, and notice that the ";" is not escaped to "%3B" in the 'milestone=' part.