Simplify Probe integration

Currently the integration "surface" is larger than it needs to be. It consists of:

• ProbeExtension
• Probe (Weld Service)
• ProbeFilter
• ProbeServlet

This all needs to be configured / initialized by an integrator for probe to work correctly. We should be able to simplify this to:

• a filter - combining both ProbeFilter and ProbeServlet
• an extension
  • invocation monitor integration
  • event monitor integration
  • holder for Probe's state (accessing the state from e.g. a filter is easy - beanManager.getExtension(ProbeExtension.class))