Added extra environment variable that may be passed to dylibbundler as
an environment variable DYLD_LIBRARY_PATH. (Variables are normally
to make but DYLD_LIBRARY_PATH is stripped.)

This is needed eg. for bundling CUDA (because it uses @rpath).

This will cause that unless user requests explicitly IPv4, IPv6 socket
accepting also IPv4 traffic will be opened. This fixes potential issues
when host specifies IPv4 address (or hostname resolvable to IPv4), thus
opens IPv4 socket. But the other peer uses IPv6 address of the host
which causes that the host doesn't receive anything.

fixes for typos in messages

removed double http from url

This commit fixes a deadlock that could happen if the
UltraGrid process crashed or was killed while it held a lock
to the shared memory segment used for preview.

On Windows this happened often, because Qt can't terminate a QProcess
gracefuly and needs to kill it every time.

On Windows the socket library must be initialized before use

This should fix GUI vu meter on Windows

+ fixed icon (it was previously put to the bundle without GUI)

Exit with non-zero return code if GUI build fails.

Fixes the bug that limited the maximal number to 2.