CS roadmap structure changes (trees, notations)

[Dev1Art]

Feature Description

What i suggest:

1. add topics about small o and small w in Asimptotic Notation.
2. in Trees topic - remove bfs and dfs or reorganize (cause inorder, preorder, postorder and level-order actually the same as bfs and dfs in that case). Add Morris traversals topics.
3. Add Threaded Binary Tree
4. organize how Trees divided into groups (e g by Level completion - Full, Perfect, Complete. By amount of elements - binary, ternary and so on).