Streamline JSDoc code documentation

[fschmenger]

A lot the codebase is not properly documented.
We possibly should

• Install a plugin like eslint-plugin-jsdoc and include the jsdoc/recommended rules
• Go through all components and files and add missing comments
• Make sure comments are well formatted in respect to
  • spacings
  • correct spelling, e.g. according to the JSDoc cheatsheet @param Number and @param String should be spelled with a lowercase n or s
  • uppercase / lowercase comments
  • finish with fullstops

We could also consider using the plugin for autogeneration and enhancement of our API doc.

[fschmenger]

This has been originally mentionend in #452 by @sronveaux:

As stated in your comment, JSDoc comments would deserve to be addressed where missing and I think they also should be uniformized from file to file. Some have spaces between description and @tags while some don't, descriptions sometimes start with an uppercase and sometimes not, descriptions sometimes finish with a fullstop sometimes not, etc... this is purely stylistic and perhaps not that important but sticking to the same rules everywhere makes it more readable IMHO.
The standard doesn't discuss some of these points and even some style guides like the one of Google don't talk about these neither.
Perhaps a simple way to start would be to install a plugin like eslint-plugin-jsdoc and include the jsdoc/recommended rules to see where it leads...