Add extradiskinfo switch to show extra disk info such as volume label and total disk usage

[DeepSpace2]

Added -extradiskinfo to show volume labels and total usage if more than a single disk is shown:

$ .\winfetch.ps1 -extradiskinfo -showdisks C:

$ .\winfetch.ps1 -extradiskinfo

[TMA-2]

It seems there's a small typo in this:
$totalDisksUsage = 0 is later referred to with $totalDisksUsed