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>
gradle: remove bundle-to-bundle dependency, it's not there

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
gradle: show wrapper task separately

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
gradle: the default task is now jar, which includes bundle

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
gradle: add findbugs to the build (disabled by default)

To enable, mention findbugs explicitly on the command line as a
task to run.

Use the -PCI command line option to generate findbugs xml reports
instead of html reports.

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
gradle: improve the custom build setup

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
gradle: add class cycle checks

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
gradle: allow individual enablement of findbugs tasks

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