Make milestone list scrollable and support more milestones

[veger]

By embedding the milestone elements in a (virtual) scroll list, it will be possible to scroll them, which lifts the restriction of only allowing 60 milestones.

Background: when playing extensive mod packs with lots of new/unknown technologies it is often hard to determine the research path to take. I find it convenient to add a lot (all) technologies to the milestone list, so YAFC shows which technologies I should research to unlock some item/recipe.

This PR also fixes the original (probable) reason for this limitation: ulong can only hold 64 bits, and the Analyser uses bits to keep track of the dependencies of the milestones (and other objects). By replacing ulong with the custom build Bits class, this limitation is lifted.

To be more confident that I did not break things, I first added a (simple) test suite for milestones. Then applied the changes and with minimal changed (had to use the Bits class now) the test suite still runs properly.
Additionally, I made these changes more than a year ago (ShadowTheAge#203) and have been playing with loads/all (!) technologies of Pyanodons added to the milestones without issues:

Note that these (open) PRs are very convenient combined with this feature:

• Select multiple recipes in the full recipe lists ShadowTheAge/yafc#168
• Support filtering on Factorio type ShadowTheAge/yafc#204

I'll open PRs for these features after this one (to keep the list of open PRs reasonable)