CMake: replace Conan with find_package and add find modules

Also, necessarily coupled with this:
* add CMakeLists.txt for vendored libnyquist
* fix SoundTouch header include paths
* move nyq_reformat_aud_do_response function
* handle portSMF headers installed to portsmf or portSMF

Signed-off-by: Be <be@mixxx.org>

cmake-modules/FindPortTime.cmake

@@ -0,0 +1,62 @@
+# Copyright (C) 2001-2020 Mixxx Development Team
+# Distributed under the GNU General Public Licence (GPL) version 2 or any later
+# later version. See the LICENSE.txt file for details.
+
+#[=======================================================================[.rst:
+FindPortTime
+---------------
+
+Finds the PortTime library.
+
+Result Variables
+^^^^^^^^^^^^^^^^
+
+This will define the following variables:
+
+``PortTime_FOUND``
+  True if the system has the PortTime library.
+``PortTime_INCLUDE_DIRS``
+  Include directories needed to use PortTime.
+``PortTime_LIBRARIES``
+  Libraries needed to link to PortTime.
+
+Cache Variables
+^^^^^^^^^^^^^^^
+
+The following cache variables may also be set:
+
+``PortTime_INCLUDE_DIR``
+  The directory containing ``porttime.h``.
+``PortTime_LIBRARY``
+  The path to the PortTime library.
+
+#]=======================================================================]
+
+find_library(PortTime_LIBRARY
+  NAMES porttime
+  DOC "PortTime library"
+)
+mark_as_advanced(PortTime_LIBRARY)
+
+find_path(PortTime_INCLUDE_DIR
+  NAMES porttime.h
+  PATH_SUFFIXES portmidi porttime
+  DOC "PortTime include directory")
+mark_as_advanced(PortTime_INCLUDE_DIR)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(
+  PortTime
+  DEFAULT_MSG
+  PortTime_LIBRARY
+  PortTime_INCLUDE_DIR
+)
+
+if(NOT TARGET PortMidi::PortTime)
+  add_library(PortMidi::PortTime UNKNOWN IMPORTED)
+  set_target_properties(PortMidi::PortTime
+    PROPERTIES
+      IMPORTED_LOCATION "${PortTime_LIBRARY}"
+      INTERFACE_INCLUDE_DIRECTORIES "${PortTime_INCLUDE_DIR}"
+  )
+endif()