Alerts Update

Implemented base class Alert.
Implemented Alerts for Cheering Bits, Following, Raid Alert, and
Subscription alerts.
Added Fonts and Video media.

UI/Alerts/follow_alert.gd

@@ -0,0 +1,16 @@
+@tool
+extends Alert
+class_name FollowAlert
+@onready var main_text: Label = %MainText
+@onready var timeline: AnimationPlayer = %Timeline
+
+var _chatter: String = "None"
+
+func setup(chatter: String) -> void:
+	_chatter = chatter
+
+# Called when the node enters the scene tree for the first time.
+func _ready() -> void:
+	main_text.text = _chatter
+	if Engine.is_editor_hint(): return
+	timeline.play(&"default")