Update Qt5 ports to 5.9.3.

This took quite a lot of time because Qt's own build system underwent
several changes in 5.8.0 that took a while to adapt to.

And, of course, qt5-webengine is a behemoth that we need to patch like crazy
due to its bundling of Chromium. In fact, most of the Chromium patches in
qt5-webengine have been imported with no changes from www/chromium@433510
("www/chromium: update to 56.0.2924.87").

New port: accessibility/qt5-speech

Bigger changes to Qt5 ports we had to make:
- Qt now allows using a configure.json file to define configuration options
  and specify configuration checks that can be done when qmake is invoked.

Update Qt5 to 5.7.1, and unify the Qt4 and Qt5 ports some more

* Update Qt5 to 5.7.1
* Move Qt4 binaries to lib/qt4/bin
* Move Qt5 libraries to lib/qt5/lib
  By moving the libraries we should finally be able to get rid of the inplace
  upgrade bug (see ports bugs 194088, 195105 and 198720):  when Qt5's libraries
  were lying in /usr/local/lib, which would often get added by pkgconfig to the
  linker paths via dependencies, the already installed libraries were linked
  against, instead of the ones that were being built. This forced us to make
  sure, that -L${WRKSRC}/lib was always coming before -L/usr/local/lib in the
  linker flags. With this change this should no longer be the case.
* Rename some ports to match the rest (foo-qtX -> qtX-foo)
* Depend on new port misc/qtchooser [see UPDATING & CHANGES]

There are several new Qt5 ports which all have been created by Marie Loise
Nolden
<nolden@kde.org>. Thanks again.

PR:		216797
Exp-Run by:	antoine
Reviewed by:	rakuco, mat, groot_kde.org
Approved by:	rakuco (mentor)
Differential Revision:	https://reviews.freebsd.org/D9213