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.
 


It was required because the resolving object itself uses another property object to get a string from it. To avoid endless loops it has to acces the original function. 
But this isn't required anymore, since i refactor the function (see other comment).