Always generate components by default

[laeubi]

Currently a user must actively enable the generation of DS components from XMLs what is quite annoying, as from a user POV I can't think about a case where I want to annotate a component but don't get the xml generated.

Especially as we already have the annotations on the classpath by default, and when using automatic manifest generation they are already generated always.

Together with

• Enhance the BuildContext with the discovered annotations eclipse-jdt/eclipse.jdt.core#676

we now also have an efficient way to know if a project has any annotation of interest.

Therefore my suggestion is to if not explicitly disabled we enable them by default with useful defaults.

[laeubi]

It would be good for this "default generated items" to be placed in the output folder instead, this is currently blocked by:

• dev.properties provided extra classpath items are invisible to  eclipse-equinox/equinox#389

this would save us from making the workingtree dirty and modify build.properties files.