Customizable app name and locations

[3v1n0]

Allow to customize data locations and app name at compile time.

This allows better snappification of Remmina (and potentially the ability of distribuiting multiple versions togeter, using different app names depending on channels, such as org.Remmina and org.Remmina.Unstable).
See https://github.com/3v1n0/Remmina-snap.

[giox069]

Tested on ubuntu 16.04 in a development environment, seems to be fine.

[antenore]

Tested on Ubuntu 16.04 as well, plus FreeBSD and Fedora 23/24 for compatibility reasons.

Everything is fine. For me can be merged.

[3v1n0]

Thanks @antenore and @giox069, Snap branch (https://github.com/3v1n0/Remmina-snap) updated... Once you want to take ownership for it, just let me know. Also you might want to register the 'remmina' name in the ubuntu store (you can use snapcraft tool or the apps portal).

[giox069]

Thank you again @3v1n0 , we will proceed as soon as we can.

[3v1n0]

@giox069 no problem...

Let me know in case you'd need help for setting up travis jobs (if you don't want to use launchpad for this) to do automatic uploads on each commit to the edge channel and release tags to the stable one (an example is at https://github.com/elopio/hashicorp-snaps)...