Use Travis CI to test flatpak recipes

[amtlib-dot-dll]

@antenore I made several changes including reverting the recipe and modifying .travis.yml for automatic flatpak builds. Is there any problem?

cc @larchunix

5b0450e#commitcomment-28518966

[antenore]

Cool! Thanks!
One thought, recently we have removed the snap build from travis, because it was taking too long and often going in timeout.
So let's see how it'll work out. For snap builds we have moved the process on snapcraft. If it'll take too long is it possible to do the same on flathub?

[amtlib-dot-dll]

We can disable it by removing it from the matrix section in .travis.yml file, however Travis CI allocates 50 minutes to every job and according to the log every job just takes less than 20 minutes. I haven't used snap, but I guess that snap would be even more quicker? Since flatpak requires you to compile everything by yourself.

[antenore]

OK, I'm going to merge this, let's see how things will work.

[amtlib-dot-dll]

Still, I wonder why the snap builds are slow 🤔