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/Findid3tag.cmake

@@ -0,0 +1,76 @@
+# 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:
+Findid3tag
+----------
+
+Finds the id3tag library.
+
+Imported Targets
+^^^^^^^^^^^^^^^^
+
+This module provides the following imported targets, if found:
+
+``id3tag::id3tag``
+  The id3tag library
+
+Result Variables
+^^^^^^^^^^^^^^^^
+
+This will define the following variables:
+
+``id3tag_FOUND``
+  True if the system has the id3tag library.
+``id3tag_INCLUDE_DIRS``
+  Include directories needed to use id3tag.
+``id3tag_LIBRARIES``
+  Libraries needed to link to id3tag.
+``id3tag_DEFINITIONS``
+  Compile definitions needed to use id3tag.
+
+Cache Variables
+^^^^^^^^^^^^^^^
+
+The following cache variables may also be set:
+
+``id3tag_INCLUDE_DIR``
+  The directory containing ``id3tag.h``.
+``id3tag_LIBRARY``
+  The path to the id3tag library.
+
+#]=======================================================================]
+
+find_package(PkgConfig QUIET)
+if(PkgConfig_FOUND)
+  pkg_check_modules(id3tag id3tag)
+else()
+  find_path(id3tag_INCLUDEDIR
+    NAMES id3tag.h
+    DOC "id3tag include directory")
+
+  find_library(id3tag_LINK_LIBRARIES
+    NAMES id3tag
+    DOC "id3tag library"
+  )
+
+  find_package(ZLIB REQUIRED)
+  list(APPEND id3tag_LINK_LIBRARIES ZLIB::ZLIB)
+endif()
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(
+  id3tag
+  DEFAULT_MSG
+  id3tag_LINK_LIBRARIES
+  id3tag_INCLUDEDIR
+)
+
+if(id3tag_FOUND)
+  if(NOT TARGET id3tag::id3tag)
+    add_library(id3tag::id3tag INTERFACE IMPORTED)
+    target_link_libraries(id3tag::id3tag INTERFACE "${id3tag_LINK_LIBRARIES}")
+    target_include_directories(id3tag::id3tag INTERFACE "${id3tag_INCLUDEDIR}")
+  endif()
+endif()