Use correct SI units in output of `xbps-install` and `xbps-remove`

[camoz]

• Package size numbers (and maybe other sizes) are calculated/displayed in units based on powers of 2 (e.g. KiB), but the wrong unit is displayed, namely units based on powers of 10 (e.g. KB).
• There should be a space between the number and the unit suffix which is 1) standard according to SI and 2) more readable.