use Salt in a faster way

There are some tricks you can use to speed up the creation of Salt graphs and their memory size. 

* you should provide names for all elements, otherwise Salt will choose one by doing long calculations
* Use as less labels (thus SFeatures) as possible: we now combine the relANNIS relevant features into one feature
* tweak the XMI serialization parameters
* do not copy lists from getter functions of Salt as a security precaution that are already either read-only or a copy of the original list