Fix: Calculation of initial engine age was inaccurate. (#11660)

Engine age in months was calculated as the difference in days / 32, instead of the actually difference in months. This would result in engines being artificially younger if a game was started at a later date.

Codechange: automatic adding of _t to (u)int types, and WChar to char32_t

for i in `find src -type f|grep -v 3rdparty/fmt|grep -v 3rdparty/catch2|grep -v 3rdparty/opengl|grep -v stdafx.h`; do sed 's/uint16& /uint16 \&/g;s/int8\([ >*),;[]\)/int8_t\1/g;s/int16\([ >*),;[]\)/int16_t\1/g;s/int32\([ >*),;[]\)/int32_t\1/g;s/int64\([ >*),;[]\)/int64_t\1/g;s/ uint32(/ uint32_t(/g;s/_uint8_t/_uint8/;s/Uint8_t/Uint8/;s/ft_int64_t/ft_int64/g;s/uint64$/uint64_t/;s/WChar/char32_t/g;s/char32_t char32_t/char32_t WChar/' -i $i; done

Fix #10032: Capacities of articulated vehicles in build window

See also: #9954

Change: Add extra random seed to StartupEngines().

This means that calling reset_engines will rerandomise introduction dates
and reliability.

Probably not necessary.

(svn r15541) -Revert (r15399): 'v->cargo_type' is also used in other places, which cannot accept CT_INVALID.
-Codechange: Add Engine::GetDefaultCargoType() and Engine::CanCarryCargo() and use them.
-Fix [FS#2617]: When articulated parts have no available default cargo, use the cargo type of the first part for livery selection.
-Change: To decide whether a vehicle is refittable do not test its current capacity for being zero, but always use the 'capacity property'.
Note: The property is used unmodifed without calling CB 15/36. By setting it to a non-zero value and returning zero in the callback vehicles can be refitted to/from zero capacity for e.g. livery effects.
Note: It is intentional that you cannot control refittability by CB 36.

(svn r14683) -Change: only say a engine/vehicle is refittable when it can be refitted to at least two cargo type or when it has subcargos.
NOTE: it is still possible that a vehicle is marked refittable when there is nothing to refit to, e.g. when only one subcargo is available but that cannot be determined without a vehicle chain.