Add a Statistics tab with a card for every soundtrack

Part of #41. The top bar has Quiz and Statistics tabs instead of the
Statistics button. The Statistics tab replaces the quiz below the top bar
(the song keeps playing) and shows every soundtrack as a card with its
plays, last played date and most and least played songs, loaded from the
new GET /api/v1/statistics/soundtracks. The cards can be searched (with
the Search popup's matching, now in SoundtrackSearch), filtered on played
or never played, and sorted A-Z, Z-A, most or least played. Clicking a
card opens a popup with all its songs.

Screenshots of the other states only differ in the top bar, and the
layout baseline is taken again with the new statistics states.

main/main_window.gd

@@ -1,9 +1,9 @@
 class_name MainWindow
 extends Control
-## The main window: the top bar, the popups opened from it and the quiz below it.
+## The main window: the top bar, the popups opened from it, and below it the quiz or the
+## statistics, depending on the chosen tab.
 ##
-## Everything that is not part of a quiz lives here, so other views can be added next
-## to the quiz later.
+## Everything that is not part of a quiz lives here.
 
 ## Dims the window behind an open popup and keeps clicks from reaching the buttons under it.
 var popup_backdrop: PopupBackdrop
@@ -16,8 +16,8 @@ var popup_backdrop: PopupBackdrop
 @onready var qr_popup: QRPopup = %QRPopup
 @onready var about_popup: AboutPopup = %AboutPopup
 @onready var log_popup: LogPopup = %LogPopup
-@onready var statistic_popup: PopupPanel = $StatisticsPopupPanel
-@onready var statistic_label: Label = %StatisticsLabel
+@onready var statistics_view: StatisticsView = $StatisticsView
+@onready var soundtrack_stats_popup: SoundtrackStatsPopup = $SoundtrackStatsPopup
 
 
 func _ready() -> void:
@@ -26,7 +26,7 @@ func _ready() -> void:
 		GameLog.debug("is_mac")
 	top_bar.search_pressed.connect(show_search)
 	top_bar.sync_pressed.connect(sync_soundtracks)
-	top_bar.statistics_pressed.connect(get_statistics)
+	top_bar.tab_selected.connect(show_tab)
 	top_bar.shortcuts_pressed.connect(show_shortcuts)
 	top_bar.about_pressed.connect(show_about)
 	top_bar.qr_pressed.connect(show_qr)
@@ -35,6 +35,7 @@ func _ready() -> void:
 	sync_popup.sync_finished.connect(_on_sync_finished)
 	quiz.server_changed.connect(search_popup.get_list_of_soundtracks)
 	quiz.event_logged.connect(log_popup.add_log_row)
+	statistics_view.soundtrack_selected.connect(soundtrack_stats_popup.show_soundtrack)
 
 	search_popup.get_list_of_soundtracks()
 
@@ -55,7 +56,8 @@ func _input(event: InputEvent) -> void:
 
 
 func _popups() -> Array[BasePopup]:
-	return [search_popup, sync_popup, qr_popup, shortcuts_popup, about_popup, log_popup]
+	return [search_popup, sync_popup, qr_popup, shortcuts_popup, about_popup, log_popup,
+			soundtrack_stats_popup]
 
 
 func show_search() -> void:
@@ -78,11 +80,15 @@ func show_qr() -> void:
 	qr_popup.open()
 
 
-func get_statistics() -> void:
-	GameLog.debug("get_statistics")
-	statistic_popup.visible = true
-	statistic_label.text = "Total amount of soundtracks in the playlist: " \
-			+ str(search_popup.soundtracks.size())
+## Shows the quiz for [code]&"quiz"[/code] or the statistics for [code]&"statistics"[/code].
+## A hidden quiz keeps playing its song.
+func show_tab(tab: StringName) -> void:
+	GameLog.debug("show_tab ", tab)
+	top_bar.select_tab(tab)
+	statistics_view.visible = tab == &"statistics"
+	quiz.visible = !statistics_view.visible
+	if statistics_view.visible:
+		statistics_view.refresh()
 
 
 func sync_soundtracks() -> void:
@@ -100,3 +106,5 @@ func _on_sync_finished() -> void:
 	GameLog.debug("_on_sync_finished")
 	search_popup.get_list_of_soundtracks()
 	quiz.on_sync_finished()
+	if statistics_view.visible:
+		statistics_view.refresh()