Configurable Pass/Mail Level

[colonyan]

    Being able to modify city building's passenger and mail level
    would open new game behavior possibilities.

    Currently, commercial tagged one get X2 for mail level, industry one for half.
    Passengers level is same/proportional to base level represented by /1000 of
    removal cost.    (or something similar to this)
   
    For example, one can apply x5 passenger value of base level for commercial
    and 1/2 for residential to make commercial city building much more attractive
    compared to others.

    This will make more definite passenger flow pattern
    if certain city contain more one type among com/res/ind city building with
    more same type coagulation inside the city.

    Some mixture of these new parameters can create more interesting passenger
    /mail flow variation possibilities.
   
    (new parameter like modifiable destination percentage. which we have
    50% for city building, 33% for industry building, 17% for tourist attraction)

    (another parameter is different city prefer building one type among res/com/ind
    than the mixture of all, all the way keeping res/com/ind balance all map wise)