* Change the getCallout method to findCallout and return a list of registered callout for a column. Callout is not a singleton service and developer can register multiple callout per column
* Make consistent with current semantic where callout is not invoke if record is processed and not always updateable.
* Make consistent with current semantic where only non empty string return from the callout instance is return to the caller as an error message string.
Embed ADempiere in Equinox OSGi
* Status: Swing client can be started in Equinox - not tested much
* turned base, client and tools projects into bundles
* sorted out some glitches in resource loading
* a copy of Adempiere class in client was required to correctly fire up swing
* first ideas for the service interfaces (see base/org.adempiere.base package)
https://sourceforge.net/tracker/?func=detail&aid=2700937&group_id=176962&atid=879334