Allow hiding milestones in a milestone path

[#1]

Allow hiding milestones when they are no longer relevant, without removing them from the milestone path to preserve historic data.

Just like the functionality to hide/unhide options in a dropdown field, I suggest implementing a similar feature for milestones. This would keep our milestone paths clear and concise, and eliminate the need to create new milestone paths.

Additionally, the milestones view on the project page should be made more flexible as the current layout appears rigid and outdated.

[#2]

Oooh, I like this one!