Replace SHA with PBKDF2-SHA512+Salt

Uses the MINOR_VERSION (which until now it was 0) to upgrade the hash
from SHA to PBKDF2-SHA512+salt.
I would have loved to completely replace it once the wallet is ported
to the new hashing but because of kwalletd code that is not possible
without a bigger rewrite.

There are 2 reasons for this patch:
1-We avoid using our own implementation of SHA
2-We use a modern hashing technique

I'm cooking more patches to use the system user password to open the
wallet, we want that password to be hashed using PBKDF2_SHA512
for security reasons.

REVIEW: 115497

NOTE by valir: this was not backported to 4.12 branch and because of
that my CBC patch let the sources into an incosistent state in respect
with the 4.14 branch. I cherry-picked this commit here, on the 4.12
branch an now the problem is gone, confirmed using the "testcase"
wallet provided with the bug report.

BUG: 343718