first implementation of span name filters

![screen shot 2014-09-02 at 10 48 05](https://cloud.githubusercontent.com/assets/4069725/4115884/3c349676-327e-11e4-9bef-ed039787fece.png)

When the path contains UUID, or Long values, the list of span names explode,  In production we see that cassandra is struggling when a huge amount of different span names needs to be inserted into the database.
I created the possibility to add a filter to the span name creation.   For the spring rest-easy you can add them by simply creating a config class in your project.  Jersey implementation currently takes no filter.  Two filters are implemented: No filter and Filter out numeric values which filters path/ab1234/path into path/<numeric>/path.  Of course a custom filter for your application can be made.