docker feature not included in Marketplace entry for JBoss Tools

Because we removed the docker feature and replaced it with the docker plugins in order to avoid the odious problem of a disabled update site appearing in Eclipse's list of Available Update Sites, we no longer have a way to provide the docker tooling via our Marketplace entry.

Solution:

1. Stop caring if there's an extra disabled update site in Eclipse when we install JBT (there's a disabled Mylyn one there too, plus 4 enabled ones for Mars, Mylyn, Eclipse, and WTP, so what's one more?).
2. Use the Docker Tooling feature in JBT's CoreTools category & on the Marketplace entry (as we did for Beta2).

Then, for JBDS, we continue to just use the plugins and include them in the com.jboss.devstudio.core.feature so they're installed OOTB via the BYOE / Core feature (and also via Marketplace).

Sound good?

Alternative solutions:

a. Create a new feature wrapper, just to contain the docker plugins

b. Update some JBT plugins to depend on the docker plugins so they get installed along with the existing JBT plugin

c. do nothing