Research growth/decay

**What do you want to see?**
An option in game setup (maybe modifiable by empire wide abilities) to allow research points spent toward incomplete techs to decay each turn (or grow!) This would be a percentage of the existing saved research points.

**How would it help players?**
Discourage spending on techs that would take too long. Synergizes well with #88 and #87.

**Alternatives**
Could make it a flat amount rather than a percentage?

**Screenshots and mockups**
N/A

**Things to consider**
N/A