Add snap packaging

[mardy]

No description provided.

[cdcseacave]

Great contribution! Thank you, Mardy!

[mardy]

Hi cdc! Just in case you are wondering how to test the package: make sure you have the snap command available; if not, you can follow these instructions.
Once you have snap installed, you can just run

snap install openmvs

And the package will be installed. Note that in order to avoid namespace issues, all command are prefixed with openmvs; so, for example, in order to run ReconstructMesh you'll actually need to type

openmvs.ReconstructMesh

On the positive side, one can simply type openmvs. and then press TAB twice in the terminal to see the whole list of available OpenMVS tools.