settings: Add option to guess song metadata

Add "Try to guess missing metadata" option to the Song Metadata page
that controls the setting in SongPathParser.

src/core/tagreaderclient.cpp

@@ -58,6 +58,8 @@ TagReaderClient::~TagReaderClient() {}
 
 void TagReaderClient::Start() { worker_pool_->Start(); }
 
+void TagReaderClient::ReloadSettings() { path_parser_->ReloadSettings(); }
+
 void TagReaderClient::WorkerFailedToStart() {
   qLog(Error) << "The" << kWorkerExecutableName << "executable was not found"
               << "in the current directory or on the PATH.  Clementine will"

src/core/tagreaderclient.h

@@ -47,6 +47,7 @@ class TagReaderClient : public QObject {
   static const char* kWorkerExecutableName;
 
   void Start();
+  void ReloadSettings();
 
   ReplyType* ReadFile(const QString& filename);
   ReplyType* SaveFile(const QString& filename, const Song& metadata);

src/ui/songmetadatasettingspage.cpp

@@ -21,6 +21,8 @@
 #include <QThread>
 
 #include "core/player.h"
+#include "core/songpathparser.h"
+#include "core/tagreaderclient.h"
 #include "ui/iconloader.h"
 #include "ui_songmetadatasettingspage.h"
 
@@ -52,6 +54,14 @@ void SongMetadataSettingsPage::Load() {
       QString::number(max_numprocs_tagclients));
 
   s.endGroup();
+
+  s.beginGroup(SongPathParser::kSongMetadataSettingsGroup);
+  bool guess = s.value(SongPathParser::kGuessMetadataSetting,
+                       SongPathParser::kGuessMetadataSettingDefault)
+                   .toBool();
+  ui_->guess_metadata->setCheckState(guess ? Qt::Checked : Qt::Unchecked);
+
+  s.endGroup();
 }
 
 void SongMetadataSettingsPage::Save() {
@@ -61,6 +71,15 @@ void SongMetadataSettingsPage::Save() {
   s.setValue("max_numprocs_tagclients", ui_->max_numprocs_tagclients->value());
 
   s.endGroup();
+
+  s.beginGroup(SongPathParser::kSongMetadataSettingsGroup);
+
+  s.setValue(SongPathParser::kGuessMetadataSetting,
+             ui_->guess_metadata->checkState() != Qt::Unchecked);
+
+  s.endGroup();
+
+  TagReaderClient::Instance()->ReloadSettings();
 }
 
 void SongMetadataSettingsPage::MaxNumProcsTagClientsChanged(int value) {

src/ui/songmetadatasettingspage.ui

@@ -56,6 +56,16 @@
      </layout>
     </widget>
    </item>
+   <item>
+    <widget class="QCheckBox" name="guess_metadata">
+     <property name="toolTip">
+      <string>Try to extract title, artist, and album from file path.</string>
+     </property>
+     <property name="text">
+      <string>Try to guess missing metadata</string>
+     </property>
+    </widget>
+   </item>
    <item>
     <spacer name="verticalSpacer">
      <property name="orientation">