Sharetool: Allow node/area ownership transfer to specific account

[S-S-X]

Allow using sharetool to change node and area ownership to selected account instead of default shared account.

How to implement:

• Add formspec through info function for extra functions
• Formspec should have input for new owner
  • Possibly with drop down menu that contains logged in players
• Check if new owner actually exists
• Targeting air should check if there is protected area and transfer everything in that area to selected player account, also area ownership
  • Either disallow updating large areas because that can cause server freeze
  • or handle large areas asynchronously, requires async worker and would be good to lock area until transfer is completed
    • Handle cases where server is restarted during operation, requires persistent storage with information about area, progress, new owner.
• Targeting node not registered for sharetool should do things stated above, same behavior as air nodes
• Update node infotext after owner is updated
  • Technic chests
  • Protector block/badge
  • Locked chest
  • Locked steel door
  • Locked steel trapdoor
  • Travelnet / travelnet elevator

[S-S-X]

First version operating inside static radius 5 cube, checks protections on all corners and middle, corners should already be enough to handle protector blocks.
Formspec receive handler will check everything again just before starting ownership updates and therefore should be safe.

Also updated formspec API to be nicer, hating formspecs a lot less now 😄
New formspec API is still buggy and requires tests but it is usable even while box sizes are not exactly accurate, there's no real grouping for elements and only supports size/button/table/field.

[S-S-X]

Last change introduced bug #94 which can freeze server if tool is used without care.