add genfont2 and unifont build-dependency

add genfont2 and unifont build-dependency

this patch introduces a new tool to generate font data
it uses a new build-dependency, namely unifont, which is an opensource
font with printable charachters for the unicode range from
0x0000 to 0xFFFF

we generate a file which is easily mmap'able and has the same bitformat
we used before (minus the codepoint -> address translation)

note that some characters are using 2 columns as width, so to have a
static lookup, we need to make each character 32 byte long
(1 byte per line, 16 lines per terminal column)

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>