Rename qt.git to qt4.git, qt5.git to qt.git

As recently discussed on the developer@ mailing-list, it is time to rename our superrepo to qt.git; however, before we can do that, we need to move the existing qt.git (which contains Qt 4) to qt4.git. Judicious use of symlinks shall be needed, to smooth the transition.
This must be done in several steps:

1. Rename qt4.git to qt.git, create a symlink qt.git temporarily pointing to qt4.git
2. Announce on the development@ mailing-list that you have done this.
3. Update all wikis, documentation and other publicly visible information sources that currently mention qt.git to mention qt4.git
4. Wait a week or three
5. Remove that symlink
6. Wait a week or three
7. On (at least) each of Gerrit, code.qt.io and GitHub, rename qt/qt5.git to qt/qt.git and create a symlink (does GitHub have a way to create such an alias ?) named qt/qt5.git pointing at it
8. Announce on the development@ mailing-list that you have done this and encourage everyone to update all their git remotes accordingly.
9. Update all wikis, documentation, etc. as before, and all build, provisioning and configuration scripts – including qt5/init-repository and scripts in qtrepotools and qtqa – to reference qt/qt.git instead of qt/qt5.git and to refer to the supermodule's checkouts as qt rather than qt5.
10. On some quiet Sunday morning (it would probably be worth announcing in advance on development@), when you're feeling brave and think you've completed the above, temporarily remove the qt5.git and have the Coin folks do a dry-run of a release build-and-test of the whole of Qt. Restore the symlink. If anything went wrong, go back one step and try again. If nothing goes wrong:
11. File a task against Qt 7 to remove the qt/qt5.git symlinks.