gradle: Allow bnd_defaultTask property to specify multiple tasks

The tasks names are comma separated.

Fixes #574.

Signed-off-by: BJ Hargrave <bj@bjhargrave.com>
Merge pull request #575 from bjhargrave/issue574

gradle: Allow bnd_defaultTask property to specify multiple tasks
[javadoc] After discussion about isOk() and isFailOk() improved doc.
[core] Added merge facility to Parameters
Bnd Driver and gestalt 
Added support for an environment driver of bnd. This driver should be set when bnd is started by for example gradle or ant. The driver can be overridden with the -bnd-driver property.

The gestalt facility is a description of the environment. It contains aspects like batch, ci, etc. that can easily be tested for.