Fixes the bug that limited the maximal number to 2.

Refer to commit b45bb22c

Template parameter was dubious under MSW (unable to deduce).

This behaves better with Wayland backend.

Fixed missing console output caused by -mwindows flag from SDL2
pkg-config.

Added options to:
- choose driver and renderer
- disable sync on VBlank

Would not work for hosts with IPv6 records only. Further it
overrides system 4/6 preference.

Get entirely rid of licensing stuff - we do not explicitly license
UltraGrid.

Reconfiguration was not entirely ok - if we are reconfiguring to bigger
frames, there may be some frames in progress which then will be copied
to framebuffer with the size of the reconfigured (bigger) frame size.