Establish a nightly build against Theia latest main branch

[JonasHelming]

We recently discussed process improvements to better support adopters to upgrade to new Theia versions. One thing we decided on is to discovered potential breaks as early as possible so that we can either avoid them or update the migration guide. As Theia Blueprint adopts Theia, we discussed the idea of having a nightly build of Blueprint against the latest state of Theia (main branch). It would discover, whether BluePrint still builds and the basic tests still run. If this build fails, an issue should be reported back to Theia, so we must establish a process to watch the build

Subtasks

• [x] Set up build that notifies on failures and runs daily
• [x] Compile for all platforms
• [x] Run tests on Windows
• [ ] Run tests on Linux
• [ ] Run tests on MacOS
• [ ] Add a Build-Status-Badge to README
• [ ] Define process for next branch (allow changes only via PR? Force push should still be possible? See https://github.com/eclipse-theia/theia-blueprint/pull/170#issuecomment-969102360)
• [ ] Fix indent/formatting in next/Jenkinsfile

Build Job : https://ci.eclipse.org/theia/job/theia-next/job/master/

[koegel]

Sounds like a good idea to me :), @jfaltermeier What do you think?

[jfaltermeier]

Sounds good to me. Building against master branch means depending on the next-versions of theia published to npm I guess?