Resolving properties

A decorator for Properties, which allows to usage of tokens in property string variables. 

For example:
```INI
[section]
val1=${prop.property.section.val} 
val2=${env.SERVER_PROFILE}
```

Also a default value can be supplied:
${prop.property.section.val|default}
If the token can't be resolved (missing property/missing env var) and there is no default value, an exeption will be thrown.
 


Looking at this, I think it might be better to have the decorator decorate the `util.PropertyAccess` interface (which is implemented by `util.Properties` as well as `util.CompositeProperties`), so it will handle both cases; at the same time, you'd not need to implement those ugly methods.