APMRouter Server ManagedMetrics Issues - Round 1

[Nicholas Whitehead]

Add type level annotation for @MetricGroup within which all the @ManagedMetric metrics will be published.
Make sure values in @MetricGroup(groupName), @ManagedMetric(category) and @ManagedMetric(displayName) can support embedded "/" characters so multiple metric namespace segments can be derived from one annotation attribute.
Support annotation attribute tokens so values can be resolved at runtime:

• ${f:x} : The value of the field "x"
• ${a:x} : The value of the attribute "x"
• ${bean} : The name of the spring bean
• ${o:x} : The value of the property "x" in the bean's ObjectName