Removed dependencies on Gathering Storm and Rise and Fall.

- Added Epic Eras as a completely different Game Speed option, rather than overwriting the Epic pace.
- Era length changes are reflected in an increased Era Score requirement for Normal / Golden Ages.
- Slightly reduced costs of starting techs to help the player when just starting the game.

Updated cost multiplier for Epic Eras, which means the techs and civics should have the normal "extended eras" feel as the game progresses.

v1.0