options handling refactored; fixes #29

well, I liked the concept proposed by Quinton in the bug comments pretty much. So followed it with some exceptions, namely:
- effective value is computed eagerly (during initialization => should be more performant)
- no writing of spy.properties provided by p6spy (I consider it beeing input of config => no updates provided), this can save us from quite some trouble related to problems on save, ... 
- jmx changes are not persisted across reloads

Any objections?