modification of query language

[remi128]

the current implementation of query definitions has some limitations regarding nested and / or clauses. Additionally the interpretion of .field, .and / .or was intransparent. Because of that a new query language is defined, where the result is an object tree, which is then translated into the suitable database specific idiom and action. This will lead into a constellation like:

new And(new Condition("firstname","Max"),new Condition("lastname","Mustermann"),new Or(new Condition("birthday",null), new Condition("age","<=","30))

[remi128]

finished by stefan, merged into develop branch