Merge separate coordinate variables with a struct

In englobs.h some info that store coordinates had separate variables for
the x coordinate and the y coordinates (for example: mappoint_array_x[]
and mappoint_array_y[]). With the use of a new type Map_Coord to hold
both coordinates we can merge each of these variables (or arrays) into
one variable. This has been done in the case of mappoint_array[],
last_built, markets[] and substations[].

Also, the variables numof_markets and numof_substations, that stores the
number of elements in their related arrays, has been changed its type
from int to unsigned int to reflect the fact.
Moving Map_Point_Info type to engglobs.h

Moves Map_Point_Info type to engglobs.h, where it belongs. This doesn't
resolve the dependecy yet, but it's one step ahead.
Moving declarations out of lin-city.h

The declarations (#defines mainly) in lin-city.h that are only used in
engine.c or simulate.c are moved into the source file.
Removed duplicated declarations in cliglobs.h

In cliglobs.h there are some variable declarations that are also
declared in engglobs.h (where they belongs). Removing this useless
externs means to include englobs.h header in some additional source
files than require them.