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/FindSndFile.cmake

@@ -0,0 +1,63 @@
+# 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:
+FindSndFile
+-----------
+
+Finds the SndFile library.
+
+Imported Targets
+^^^^^^^^^^^^^^^^
+
+This module provides the following imported targets, if found:
+
+``SndFile::SndFile``
+  The SndFile library
+
+This will define the following variables:
+
+``SndFile_FOUND``
+  True if the system has the SndFile library.
+
+#]=======================================================================]
+
+find_package(PkgConfig QUIET)
+if(PkgConfig_FOUND)
+  pkg_check_modules(SndFile QUIET sndfile)
+else()
+  find_path(SndFile_INCLUDEDIR
+    NAMES sndfile.h
+    PATH_SUFFIXES sndfile
+    DOC "SndFile include directory")
+
+  find_library(SndFile_LINK_LIBRARIES
+    NAMES sndfile sndfile-1
+    DOC "SndFile library"
+  )
+endif()
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(
+  SndFile
+  DEFAULT_MSG
+  SndFile_LINK_LIBRARIES
+  SndFile_INCLUDEDIR
+)
+
+file(STRINGS "${SndFile_INCLUDEDIR}/sndfile.h" SndFile_SUPPORTS_SET_COMPRESSION_LEVEL REGEX ".*SFC_SET_COMPRESSION_LEVEL.*")
+if(SndFile_SUPPORTS_SET_COMPRESSION_LEVEL)
+  set(SndFile_SUPPORTS_SET_COMPRESSION_LEVEL ON)
+else()
+  set(SndFile_SUPPORTS_SET_COMPRESSION_LEVEL OFF)
+endif()
+mark_as_advanced(SndFile_SUPPORTS_SET_COMPRESSION_LEVEL)
+
+if(SndFile_FOUND)
+  if(NOT TARGET SndFile::sndfile)
+    add_library(SndFile::sndfile INTERFACE IMPORTED)
+    target_link_libraries(SndFile::sndfile INTERFACE "${SndFile_LINK_LIBRARIES}")
+    target_include_directories(SndFile::sndfile INTERFACE "${SndFile_INCLUDEDIR}")
+  endif()
+endif()