Added snap recipe

snapcraft.io is now connected to https://github.com/mana/mana and will automaticaly build the mana snap and publish it to the edge channel.

There are two known issues at this point:

• The snap prints:

  /usr/share/libdrm/amdgpu.ids: No such file or directory

  on startup. So far I was unable to figure out a fix for it and I also don't know if it actually causes any problems.

• Translations do not appear to work.