[WIP] #155 Query LENGTH for binary properties

Started working on #155 this, added the length attribute to all values.

TODO: 
- [x] write some tests to check if length is correct for all propertyTypes
- [x] Adjust LENGTH() operand to query for this attribute
- [x] Create migration script

There might be more todo's.

Does anybody have an idea about the `phpcr` namespace? Is internal correct as I now did it?