never push developments directly to master

I propose (based on request/suggestion from @coldfix), that we use the branch "testing" to push any changes, and never push them onto the master branch before they have been through the nightly builds.

Both the continuous builds and nightly builds on cdash are now building from the testing branch.

This will also allow us to push simple fixes directly onto this branch, without having to go through a merge request. And hopefully it will mean that the master branch will become more stable.