* Added Era.json and imported the data to the ruleset
* Units at start are now also determined by eras.json
* Research agreement costs now determined by json file
* Gold and Culture provided at the start are now awarded
* Can no longer build wonders that are more than two eras older than the starting era
* Default population and buildings for settlers can now be added
* Added checks for validity of eras.json file in mods
* Colors for the icons of technologies are no also saved in eras.json
* Removed constants for all era's as they have been generalized away by this PR
* Removed spurios println's
* Added compatibility for mods
* Updated the military unit you get from ruines to be the military unit you received at the start of the game
