The conversion between UYVY and YUYV is symmetric so the same function
can be used.

Use testcard_convert_buffer() for pixel format conversion to avoid messy
code that there has been.

+ removed redundant functinos
+ relicense (there remains nothing from original code now)

tv_add_usec fixes handling of 2^31 us addition overflow and the original
function, tv_add is not slower if tv_add_usec is inlined.

+ improved a bit

as it is currently in the AppImage

Copy DejaVu Sans+Mono Book+Bold explicitly + pass it a variable
UG_FONT_DIR to UltraGrid.

Ensure that DejaVu fonts are installed since create_appimage.sh expects
those fonts to be present.

Changed font location to <appimage>/usr/share/fonts - this is more
convenient location than <appimage>/usr/lib/fonts.

Disable also all other components except XiApi.

Component names decompiled from installer with 7-zip 15.05, see also
https://nsis.sourceforge.io/Can_I_decompile_an_existing_installer.

In order to prevent potential freezes that nondeterministically arise.

rand_r was marked obsolete in POSIX 2008 and it is POSIX-only.

In Windows, it contains spaces.

Set signal as progressive (not-PsF) by default - previously the value
was not touched which may be a bit misleading when DeckLink outputs
actually interlaced signal.

Issue warning that the option is set and keep user opt out from setting
this value.

Currently only testcard uses this and it checks error so no other
existing code is influenced.

Honor optional "i" suffix and do not inherit INTERLACED_MERGED from
default format.

- print reqs
- really check if enabled whenever user enforces with --enable-testcard
  extras (+ optional "all")

This partially reverts eb390d34.