Add option to conditionally show menu options by a config
Add option to remove VCR scart from main menu (default off)

As most users are using HDMI I suggest most times this option is not
required at all. Especially when it is on the main menu.
Move VRC Scart on main menu option to Videomode (av) menu
Remove obsoleted config.usage.show_vcr_scart

Sorry as I forgot to remove this in the previous commit.
listboxservice: Render picons a bit smaller

Picons are usually about 3:2 in size, or even 100:70, not likely 2:1.
So reserve 1.5*height for the icon area.
gdi/gpixmap: Implement software scaling

Not all hardware supports alphablending and/or scaling, so implement
a simple software version. Also, the software version is faster for
small images (e.g. 50x50 pixels or so) because of the overhead of
setting up hardware blitting (see previous commits on this file).
listboxservice: On closer inspection, picons are 5:3

The ocram sets use 100:60 sized, and since the skins usually don't
taks aspect ratio into account, 5:3 should be "just right". Thus
no background.
listboxservice: do not keep aspect ratio anymore

As the target has already the expected aspect ratio keeping the
aspect ratio is not required anymore. So currently it can always
be scaled without having blackfilled borders.
It might have  a disadvantage with picons that big differ from the
usual picon relations.
In addition add a margin of 8 to the service name so the service
name is not "glued" to the picon.
listboxservice: Use LoadPNG and fit it to the available space

Now that we have scaled rendering, we can skip the bulky picload
and just simply load a PNG file and render it where we need it.
This renders faster and also nullifies palette problems with borders.

Also fix compiler warnings about parentheses.
gdi/gpixmap: Move alphablend function into gRGB class

gRGB knows about endianness and converting bytes to packed long,
so making alphablending its responsibility reduces code considerably.
gdi/font.cpp: Remove unused variable width

Variable width is assigned to, but never used
gdi/gpixmap: Implement software scaling for 32-bit images

Untested.
gdi/gpixmap: Add functionality to keep aspect ratio in blitscale
Listboxservice: Use new keep aspect ratio functionality from blitscale

Possibly later the GM-EPG can also use this
gpixmap: fix typo for software scaling 32-bit images
gpixmap: simply keep aspect ratio for blit scale
gdi/picload: Fix 32-bit rendering (handle stride correctly)

Filling the "bars" at the top and bottom wasn't being done
properly, it did not take into account that stride != width.
This caused images to be rendered as if "shifted".
MultiContent: Add flag to make it possible to scale pixmaps
GME: Use new multicontact flags to scale picons and backgrounds
eListboxcontent: cosmetic as tabs and spaces were used