output human-readable memory info in `pm2 list`

It's probably a good idea to display memory info like this "22.977 MB" instead of "22977672" in pm2 list.

I also moved function "bytesToSize" to CliUx because I used it in both places, and logically it's more suited to be in CliUx... not sure though

PS: lowercase "b" looks nicer imho :)