Draft:Added method to tool base class allowing for a check if the tool was configured (any property set)

For review: @wlampl @emoyse @goetz - this is the tool-is-no-the-default check implementation we talked about earlier. It is not very optimal but we anyways do it once. This is a public method because it then gives the flexibility to call from the tool initialize or by clients like this: ATH_CHECK(m_myImportantTool->isConfigured()); Let me know if this is ok so I'll un-draft it. It may bring some attention from the core team I suppose.