Add Qt translation tools

[jlayt]

QGIS currently ships with most of the binaries needed to do plugin development within the QGIS environment, such as designer, pyuic5, and pyrcc5 to work on ui files, and pylupdate5 to extract translations using a .pro file (not so useful!).

However QGIS macOS is missing the Qt binaries lrelease to compile the ts files into qm, and linguist to edit the ts files. These would be useful to ship to make it a near complete dev environment.

To complete the dev env, compiling the help docs requires sphinx-build to be installed as well.