Release the first Janitor Beta

[jankeromnes]

We should move Janitor from Alpha to Beta once these remaining issues are fixed:

• [x] hub is auto-configured with a "rotatable" GitHub Personal Access Token (see #29)
• [ ] GitHub sign-in works (see #46)
• [ ] All containers have a fixed lifetime (somewhere between 7 days and 2 years)
• [ ] Cloud9 SDK settings and preview/run buttons are much improved (see #138, https://github.com/JanitorTechnology/c9.ide.janitorconfig/issues/6, https://github.com/JanitorTechnology/c9.ide.janitorconfig/issues/4, https://github.com/JanitorTechnology/dockerfiles/issues/32)
• [x] Deleting a container is no longer confusing (many users click on Delete several times)
• [ ] ~~Ship~~ and enable @arshdkhn1 and @nt1m's new design (see #179, #176, #160, #117, and #238)
• [x] Support multiple hostnames (to allow using jntr.io or janitor.technology interchangeably) (see #188)

[jankeromnes]

I've tentatively added the new web app design as a goal for the first Beta version. Please let me know what you think of this idea. 😄