Cleanup & Fixes for .NET 5 (#309)

- [X] Fixes several bugs
- [X] Updates more ordinal issues
- [X] Cleans up the code a bit
- [X] Turns classes static that should have been
- [X] Changes TcpServer.Instances to a HashSet

Bumps release version

Projects/UOContent/Items/Construction/Misc/Easel.cs

@@ -1,7 +1,6 @@
 namespace Server.Items
 {
-    [Furniture]
-    [Flippable(0xF65, 0xF67, 0xF69)]
+    [Furniture, Flippable(0xF65, 0xF67, 0xF69)]
     public class Easel : Item
     {
         [Constructible]

Projects/UOContent/Items/Construction/Misc/MusicStand.cs

@@ -1,7 +1,6 @@
 namespace Server.Items
 {
-    [Furniture]
-    [Flippable(0xEBB, 0xEBC)]
+    [Furniture, Flippable(0xEBB, 0xEBC)]
     public class TallMusicStand : Item
     {
         [Constructible]
@@ -31,8 +30,7 @@ namespace Server.Items
         }
     }
 
-    [Furniture]
-    [Flippable(0xEB6, 0xEB8)]
+    [Furniture, Flippable(0xEB6, 0xEB8)]
     public class ShortMusicStand : Item
     {
         [Constructible]

Projects/UOContent/Items/Construction/Misc/Screens.cs

@@ -1,7 +1,6 @@
 namespace Server.Items
 {
-    [Furniture]
-    [Flippable(0x24D0, 0x24D1, 0x24D2, 0x24D3, 0x24D4)]
+    [Furniture, Flippable(0x24D0, 0x24D1, 0x24D2, 0x24D3, 0x24D4)]
     public class BambooScreen : Item
     {
         [Constructible]
@@ -26,8 +25,7 @@ namespace Server.Items
         }
     }
 
-    [Furniture]
-    [Flippable(0x24CB, 0x24CC, 0x24CD, 0x24CE, 0x24CF)]
+    [Furniture, Flippable(0x24CB, 0x24CC, 0x24CD, 0x24CE, 0x24CF)]
     public class ShojiScreen : Item
     {
         [Constructible]