Tooltip: Implemented setting to hide the default "Sell Price" tooltip

[simonebarbieri]

This PR adds a new setting, in the Tooltip section, to hide the Blizzard default tooltip "Sell Price". This is because Auctionator offers the same information with the label "Vendor".
In my opinion the setting could be completely removed, because, again, the information is basically duplicated if you enabled the vendor tooltip, but I've implemented it just in case you prefer to give the option to keep it.

Translation lines for other languages are missing, sorry. I wanted to avoid using automated tools.

I've tested only in retail though, I'm not sure this would work in Classic.

[plusmouse]

This feature was in retail Auctionator by default, but removed after it appeared to cause blocked actions in combat.

[simonebarbieri]

Oh, sorry, I didn't know that :)
Before submitting it here as PR, I kept it as a small separate addon and it didn't create any problem, but I understand that just me by myself I'm not really a relevant test group 😅

I understand if you want to close this PR if you don't want to risk it adding it back :) I'll just keep it as separate addon!