Update call-for-papers.md

[orivasplata]

Added a bullet for Reinforcement learning on its own.

Accordingly, removed "reinforcement learning" form the parenthesised list under the bullet for Deep Learning.

In the bullet "Theory of machine learning and statistics" in the parenthesised list, separated "decision making and bandits," into "decision making," and "online learning and bandits,"

[orivasplata]

Please review the proposed edits and merge.