Race/colour rules

Non-humans are fixed colour.
Choosing a colour prevents subsequent pllayers from choosing it.
+ Made non-enumerable enums negative so EnumRange skips them.
Added Player,  Players

Only known players can log in.
Player name only used for logging in and display purposes.
Return to previous game on login

+ Added "Back to game list" link.
Fix player page tabs

Tabs now use player ID instead of name
Docs