package/mono: new package

This patch adds the complete Mono implementation. This patch builds
both the native and managed parts.

[Thomas:
 - adjust license informations
 - add missing host-gettext dependency to host-mono
 - minor formatting tweaks.]

Signed-off-by: Angelo Compagnucci <angelo.compagnucci@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>