don't touch addressbook when using secure payment-requests

- fixes #3006 by preventing addressbook changes when using
  secure payment-requests

sq
Documentation Cleanup in /Doc

Added some help text, and bumped version numbers.

Added a Readable Index for /Contrib

Fixing /Contrib Index URLs

Revert Version Numbers.
make BitcoinAmountField::setReadOnly() usable

- use it for secure payment-requests (this change allows a copy&paste of
  the amount and looks a little nicer than just a disabled GUI element)
Merge pull request #3085 from super3/master

Documentation Cleanup and Contrib Index
Broken Link in /Doc README

#3092 removed readme-qt.md, but it was still listed in the index for the /doc README.
Merge pull request #3097 from super3/master

Broken Link in /Doc README
Merge pull request #3094 from Diapolo/btcamountfield

make BitcoinAmountField::setReadOnly() usable
Merge pull request #3069 from Diapolo/fix_addressbook

don't touch addressbook when using secure payment-requests