Reflectionzeug refinements

* Restore default behavior for property guis
* Remove flags in favor of a shared usage of options
* Add convenience accessors for property options
* Fix include style
* Remove obsolete member variables and corresponding functions from Enum- and StringProperty
* Add toVariant to PropertyGroup
I agree with the ease of use and less confusion during usage of flags.
Besides, the flag concept is not as powerful as the options (since flags only support 2 states, boolean options support 3).
Additionally, you introduced two different concept where we only see one.
The last and smallest issue we saw was the negative logic with the ```disabled``` flag.
Btw, your example code can now be written as ```m_property>option("enabled", true);```.