Add travis support

Add travis support
Squashed commit of the following:

commit f9a7a1fd51dd2c857fc52923be8f2e98f059f923
Author: Chocobozzz <florian.bigard@gmail.com>
Date:   Fri Oct 30 20:05:20 2015 +0100

    This is electron-prebuilt and not just electron

commit a2361482942abe4443c68e61fdcfea9bf35ede61
Author: Chocobozzz <florian.bigard@gmail.com>
Date:   Fri Oct 30 19:58:56 2015 +0100

    Let's try to change this option...

commit 7ee8bfa9bf34b0165a7ef51bc9397bf86ff54878
Author: Chocobozzz <florian.bigard@gmail.com>
Date:   Fri Oct 30 19:39:23 2015 +0100

    Explicitly say to generate a rsa key of length 2048

commit d3905aef92b537c395a9111d5d0c6f4da8b322ba
Author: Chocobozzz <florian.bigard@gmail.com>
Date:   Fri Oct 30 19:22:46 2015 +0100

    typo

commit 602cb774848da906ec693999484b618618f70846
Author: Chocobozzz <florian.bigard@gmail.com>
Date:   Fri Oct 30 19:21:26 2015 +0100

    Add after_failure, cache for grunt and electron

commit 79f7c7f7b7a9a0726de0b7b1af1cda69a4d401cc
Author: Chocobozzz <florian.bigard@gmail.com>
Date:   Fri Oct 30 19:10:25 2015 +0100

    increase timewait when uploading a video (for the federation)

commit 3c8dd590dd53ab2b069d6a52cd8e954156814304
Author: Chocobozzz <florian.bigard@gmail.com>
Date:   Fri Oct 30 19:00:26 2015 +0100

    install grunt-cli

commit 1b5d02fb067a7b4cde62a6dd5073b76e5f1ba269
Author: Chocobozzz <florian.bigard@gmail.com>
Date:   Fri Oct 30 18:55:23 2015 +0100

    Trigger travis build

commit ede965e1186c4dc25270c384f669f0d6749d2a9d
Author: Chocobozzz <florian.bigard@gmail.com>
Date:   Fri Oct 30 18:52:08 2015 +0100

    let's try travis