Add some limitations to protect system.

[JackyWoo]

Description Add some limitations to protect system, such as max_node_child_size, max_node_deepth etc.

Solution

Make the limitations confiurable. Below are some limitations:

max_node_child_size : max child size for a node
max_node_deepth: max deepth of data tree
max_node_name_length: max node name length
max_node_value_length: max node value length

max_connections