Nested Sets DB Tree: Manipulate database records in hierarchical trees

This class can be used to manipulate nested sets of database table records as an hierarchical tree.

It can initialize a tree, insert nodes in specific positions of the tree, retrieve node and it's parent records, change nodes position and delete nodes.

Currently the class functions can:

- Retrieve all data for node with number node id
- Retrieve data of closest parent for node with number node id
- Add new child element to node with number parent id
- Add a new element into the tree near node with number node id
- Assigns another parent parent id to a node node id with all its children
- Change position of nodes within the same parent and same level of nesting
- Swapping nodes with it's children within the same parent and same level of nesting
- Deletes element with number node id from the tree without deleting it's children, moving its children up one level
- Deletes element with number node id from the tree and all it children.
- Returns all elements of the tree sorted by left value
- Returns all elements of a branch starting from an element with number node id
- Returns all parents of element with number node id
- Returns a slightly opened tree from an element with number node id
- Sort children in a tree for order field in alphabetical order
- Makes UL/LI HTML from nested sets tree with links if needed