The term "control plane" is written as title case (e.g. Control Plane) only in this document. When it is referenced, it creates inconsistency in other documents. This commit will fix it by lower-casing the second word.
* Use Control Plane instead of Master
* improve image. The SVG was not matching the PNG, so I basically had to re-create it from scratch. I kept the visual similarities as mush as possible
* remove tautological phrase
* fix glossary references as well
* improve cluster glossary to move from Master to Control Plane
* improve english form