Several improvements to the code of CPController and its performance

A number of small optimizations to **CPController** that don't change its existing logic, but improve its performance and make the code more compact and easier to read (I hope).

To note specifically: Creating an instance of **NSNumberFormatter** is rather expensive (when done very often), thus it is now created once when creating an instance **CPController** and just re-used.

On my MBP I did see a notable improvement in CPU usage (about 25-30% in average, I believe).