Gitian fixes for 0.9.0rc1 build

- Add 'g++' package (virtualbox images don't have this by default)
- Workaround for determinism in Qt5 resources
- Pass --disable-maintainer-mode --disable-dependency-tracking to
  configure for libqrencode to avoid random errors about missing m4
  directory
- Fix typo -with-pic -> --with-pic

It is not necessary to rebuild dependencies after this commit.
Fixes #3610 and #3612.
added missing homebrew qt dependency on mac osx build documentation.
Merge pull request #3620

65615a3 Gitian fixes for 0.9.0rc1 build (Wladimir J. van der Laan)
Merge pull request #3621 from gubatron/build-osx-qt-dependency-missing

added missing homebrew qt dependency on mac osx build documentation.
Merge pull request #3613 from cozz/cozz1

[Qt] Fix nTransactionFee in qt-settings
Typo fix: `anonimized => anonymized` + `infromation => information`
Merge pull request #3627 from calvintam/fix_typos

Typo fix: `anonimized => anonymized` + `infromation => information`
-Wl,-z,relro and -z,now were wiping out environmental LDFLAGS passed in by the user.
I moved them to HARDENING_* where they belong.
Merge pull request #3634

505867a -Wl,-z,relro and -z,now were wiping out environmental LDFLAGS passed in by the user. I moved them to HARDENING_* where they belong. (Midnight Magic)
Update the address for downloading libpng

The FTP server what we get libpng from only keeps the latest version in its main folder. Older versions are in the "history" folder. Apparently version 1.6.9 has been released, so 1.6.8 has moved to the history folder.
Merge pull request #3635

12edce5 Update the address for downloading libpng (Micha)
[Qt] remove broken OptionsModel::Upgrade()