Stylise the titles of functions uniformly

[teddphil]

Feature Description

The current version (develop branch on 21st March 2020) contains different styles of function titles

• do a feature, like preprocess heart rate (preferred?)
• doing a feature or feature doing, like preprocessing heart rate
• feature done, like Data prepration
• noun, like Tools, 2nd model

Function titles are suggested to be stylised uniformly across the software.

[teddphil]

@dominikbach Could we discuss this later on, thanks.