Add travis ci

Adding the .travis.yml file make it possible to check if it compiles.
Also it would be possible to add a step to send the binary files somewhere if needed.

It would be possible to add something like `[![Build Status](https://travis-ci.org/isra17/popcorn-app.png?branch=master)](https://travis-ci.org/isra17/popcorn-app)` in the README to see if the last commit compile.
Travis ci can also check if pull request don't break the project.

It currently compiles (see https://travis-ci.org/rom1504/popcorn-app)

For it to actually works in the isra17 repo it's needed to : 
1) add this .travis.yml file (merge the pull request)
2) create a travis account
3) activate popcorn-app repo in travis

I thought it might be useful.