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.
 


I though maybe we could have this be like:

    new ResolvingProperties(new Properties($this->root.DIRECTORY_SEPARATOR.$name.'.ini'));

instead of this above; i.e. inject the decorated element, instead of just extending the base implementation (which is, btw, not the only relevant impl.).