Freeciv

Add concept of infrapoints

In this initial version:
- Added server setting infrapoints to control how many infrapoints
players are granted in the beginning. Default is 0 to disable
infrapoints feature. There's no other ways to get infrapoints.
When they are gone, they are gone
- gtk3.22-client is the only supported client. It has crude ui to
place extras on tiles
- Each player buildable extra costs 1 infrapoint to place

This is a bit daft feature in this form, but it's meant to be only a somehow working starting point for further development.