* 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
* "[+1 Gold] for each adjacent [Road]" Roadstatus can be used now in tile improvement uniques
* Added hasViewableResource check to "[stats] from every [Resource]"
* Fixed translation of nation uniques
* Eras with no researchable techs will not appear in dropdown menu in new game options
* Implemented startingUnits, aiMajorCivStartingUnits and aiCityStateStartingUnits fields in difficulty
* reassignRemovedModReferences will also reassign if nation is a City-State in current ruleset
e.g. Venice will be unselected if player unselects Civ5ExpansionMod which has it as playable civ
* "Cannot be purchased" - new unique for non-wonders and units. SS parts have it
* Update template.properties
* Update Difficulty.kt
