fixed the nodes with no children not resulting in correct format for lists

…dix tree was not thread safe,

improved the locking strategy for reading variables in the variables map,
replaced tree maps in variables map nodes to hash maps

…ot happen on every clear now

…ments' into feature/variable-storage-improvements

…ap - live view is now returned

subtree is now cleared only after all write/read operations on it are finished

improved the h2 storage configuration