Update README
Use AE spelling, fix placing of menu.

* Remove placeholders instead of translating them.
* Use default parameter.
Recode the setting of common attributes

* Common attributes of structures/units are now set with a function they both use
* Common attributes of techs/phases are now set with a function they both use
* Reduces repeated logic/code
Determine phase of units properly

Resolves #3
Add civil centre from starting entities list of {civ}.json

* This wouldn't be needed, except `sele` heroes are the only units of that civ that can build their civil center, and they are trained from that building.
   - Hence, the sele civil centre wasn't appearing in the structree until now