Un-hardcoded genital type genes

[flock-of-birds]

Merged genital type gene classes as it's been bugging me since 1.4. Should probably be merged after jaaldabaoth's update.

Reasoning:

• Reduces code repetition, likelihood of bugs, etc.
• Gives genital genes something in common other than defName, making it easier to write code that works with them as a group.
• Reduces amount of work involved in adding or changing genital genes.
• Makes it possible or other mods to add similar genes without trying to access an internal class, or even using C# in the first place.

Other changes

• Stopped tracking .csproj.user file. This allows people to define their own project settings without affecting the repo's .csproj (read: allows me to build in my own banjaxed environment without breaking it for others).
• Refactored GenitaliaUtility to mostly not depend on defNames. In particular, the GetXForGene methods were checking against an incomplete list of hardcoded defNames, so this might fix some issues in places where these are used.
  • I left GetBreastsForGene alone for now since they don't get
• Tweaked GenitalChanger to not overwrite parts if the new part would be of the same def, and so it can be used to replace just one or two parts instead of all three.

[flock-of-birds]

Included in #81.