[Commands] Add #unmemspell and #unmemspells Commands. (#1867)

- Add #unmemspell [Spell ID] command to unmemorize a spell by ID from you or your target.
- Add #unmemspells command to unmemorize all spells from you or your target.
- Cleanup #memspell command and change arguments from #memspell [Slot] [Spell ID] to #memspell [Spell ID] [Spell Gem] for easier use.
- Add #memspell [Spell ID] functionality to memorize to first open spell gem if there are any using FindEmptyMemSlot helper method.
- Rename client->FindMemmedSpellByID(spell_id) to FindMemmedSpellBySpellID(spell_id).
- Add client->FindEmptyMemSlot() helper method.
- Add $client->FindEmptyMemSlot() to Perl.
- Add client:FindEmptyMemSlot() to Lua.
- Add $client->FindMemmedSpellBySpellID(spell_id) to Perl.
- Add client:FindMemmedSpellBySpellID(spell_id) to Lua.

zone/gm_commands/unmemspells.cpp

@@ -0,0 +1,43 @@
+#include "../client.h"
+
+void command_unmemspells(Client *c, const Seperator *sep)
+{
+	auto target = c;
+	if (c->GetTarget() && c->GetTarget()->IsClient() && c->GetGM()) {
+		target = c->GetTarget()->CastToClient();
+	}
+
+	auto memmed_count = target->MemmedCount();
+	if (!memmed_count) {
+		c->Message(
+			Chat::White,
+			fmt::format(
+				"{} no spells to unmemorize.",
+				(
+					c == target ?
+					"You have" :
+					fmt::format(
+						"{} ({}) has",
+						target->GetCleanName(),
+						target->GetID()
+					)
+				)
+			).c_str()
+		);
+		return;
+	}
+
+	target->UnmemSpellAll();
+
+	if (c != target) {
+		c->Message(
+			Chat::White,
+			fmt::format(
+				"{} ({}) has had {} spells unmemorized.",
+				target->GetCleanName(),
+				target->GetID(),
+				memmed_count
+			).c_str()
+		);
+	}
+}