port to qt5-only phonon

• now requires cmake 3.5 same as libphonon
• also requires phonon 4.11+. there is no technical reason for this as the code is still backwards compatible, it does however restrict the scenarios needing QA to one!
• find and use ecm directly (instead of relying of libphonon implicilty)
• move from deprecated cmake includes implicitly inherited from libphonon to more modern variants (notably: featuresummary)
• revise the definition passing to go through a generated config.h instead to have a clearly separation of responsibility and also slightly easier to read. this excludes api switches because those need to be available as early as possible to manipulate phonon header behavior
• no longer use a crappy finder to wrap around the phonon cmake module, use or rather find it directly
• version setup now uses ecm_setup_version
• ecm is now always assumed as available (previously it was kinda optional because the qt4 build didn't use it)
• include directory handling has been revised to a) rely on imported targets b) for the extra include we need it's now scoped to our target rather than global
• no longer using legacy cmake macros for automoc and qt5-use
• the desktop file has been completely removed as it is replaced by the builtin json blob of the .so