Update it_IT.lang

Reverted https://github.com/Azanor/thaumcraft/pull/1329 as it contained many spelling errors and wrong translations.
Reimplemented https://github.com/Azanor/thaumcraft/pull/1280 changes to align it_IT to the last Thaumcraft release (most possibly Azanor could not pull this due to having already pulled the previous, causing conflicts) and corrected some spelling

TODO Reimplement those changes from the reverted pull that truly fix grammar and spelling errors :D