On Windows x64, fixed #208: GoldenDict crashes when indexing huge dictionaries.

According to Microsoft documentation, on x64 systems the virtual address space
for 32-bit process can be extended from 2Gb to 4Gb if if the application is
compiled with the /LARGEADDRESSAWARE switch.

I verified that with this switch we get full 4Gb on x64 systems and the
indexing of huge dictionaries works just fine now.

On x32 systems we can't do much though.
Custom icon support for Sound dir dictionaries - default to no custom icon