Add a devel branch and modify update.sh accordingly

[themousepotato]

Currently, deployment is done automatically. When many people are working with the same feature, we may need to merge some of the features which aren't completed to master. So, it's always better to have a devel branch which has code which is ready-to-deploy always.

[xypnox]

It should be named deploy branch instead of devel then.

[thealphadollar]

Well, let's have "devel" and "master". Devel is for developmental purposes and master is the one which is used in the website.

[xypnox]

We should also then notify everyone to send PRs to the development branch.

When deploying we can open a PR from devel to master and do a sort of common code review to check for typos etc.