[Refactor] Move parts of AddAnonInputs into helper functions.

[Zannick]

Rearranges part of AddAnonInputs_Inner into separate helper functions so it's easier to understand and also to reuse the code elsewhere. I'm not sure I fully understood the code enough to properly name the helper functions, but here they are:

• ArrangeBlinds
  • Places the real inputs and creates dummy entries for the ring.
  • Optionally adds temporary dummy sigs.
• GetKeyImage
  • Attaches the key image for a real input.
  • I made this take one at a time for ease of calling from elsewhere.
• SetBlinds
  • Does some further stuff to the blinds.

[WetOne]

utACK 42dfa73438bdfe535449e93fb6bcf93ba1d968d0

[Zannick]

Fixed the following:

• SetBlinds was called with nSigRingSize, nSigInputs reversed, causing a segfault.
• SetBlinds was accepting some vector arguments by value; now all vectors are correctly passed by reference.
• I had moved some vectors into SetBlinds cause they appeared otherwise unused, but they were storing data for other vectors and so needed to still be scoped to a longer lifetime than the others.