gradle: build v1

*NOTE* This branch will be rebased as fixes are applied.

Currently, the full bndtools build-template.xml ant file (and more) is
implemented. No custom ant tasks yet.

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
gradle: minor fix, gradle will figure this out for us

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
gradle: add build setup doc/svg

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
gradle: relative file URLs are relative to the root project

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
gradle: only create the export directory when there are runfiles

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
gradle: ignore downloaded build dependencies

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>