Refactor the command utils package

[honzaflash]

Reading through the cli folder contents I thought that the command utils were a little messy and had lot of duplicate code. I am not very experienced in Go so I am not familiar with the conventions, however, I think I made some improvements.

I thought about adding a commit with more comments for some of the individual commands but those actually have a decent amount of documentation or the function names are self explanatory.

This isn't exactly what I have been asked for but I think it demonstrates my understanding of what I studied and it might even be useful/worth merging.

• decrease amount of duplicate code
• add some comments
• update readme