Changes and fixes a lot of things

Adds a viewSign command which allows a player to see the entirety of a sign, including any part that overflows the character limit.
Changes the save structure for placeholder signs. This change was necessary to support storage of placeholders on both sides of signs, which is also implemented in this commit.
Updates Spigot
Probably fixes a few bugs

src/main/java/net/knarcraft/placeholdersigns/container/SignLineChangeRequest.java

@@ -0,0 +1,14 @@
+package net.knarcraft.placeholdersigns.container;
+
+import org.bukkit.entity.Player;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * A record of a player's request to change a sign
+ *
+ * @param player <p>The player requesting the sign change</p>
+ * @param line   <p>The line the player wants to change</p>
+ * @param text   <p>The new text the player provided for the line</p>
+ */
+public record SignLineChangeRequest(@NotNull Player player, int line, @NotNull String text) {
+}