Migrate most of CheckTilePermission to TSPlayer

TShock.CheckTilePermission(ply, x, y, paint) has been replaced with
TSPlayer.HasPaintPermission and TSPlayer.HasBuildPermission
respectively. These two methods dramatically simplify the logic required
to process build permissions.

Still todo after this commit:

1. Implement warnings for when a player fails a permission check on
build. This is probably going to be accomplished by a default argument
to the HasBuildPermission signature.

2. Create a variant that checks for ice tile permission and use like
HasPaintPermission() so as to remove the other
TShock.CheckTilePermission method.

Annoyingly, all of the existing methods that start with Check seem to
"check" if they player _doesn't_ have permission (true = no permission),
which makes nearly every call negative.

TShockAPI/TSPlayer.cs

@@ -335,6 +335,56 @@ namespace TShockAPI
 			return true;
 		}
 
+		private enum BuildPermissionFailPoint
+		{
+			GeneralBuild,
+			SpawnProtect,
+			Regions
+		}
+
+		/// <summary>Determines if the player can build on a given point.</summary>
+		/// <param name="x">The x coordinate they want to build at.</param>
+		/// <param name="y">The y coordinate they want to paint at.</param>
+		/// <returns>True if the player can build at the given point from build, spawn, and region protection.</returns>
+		public bool HasBuildPermission(int x, int y)
+		{
+			BuildPermissionFailPoint failure = BuildPermissionFailPoint.GeneralBuild;
+			// The goal is to short circuit on easy stuff as much as possible.
+			// Don't compute permissions unless needed, and don't compute taxing stuff unless needed.
+
+			// If the player has bypass on build protection or building is enabled; continue
+			// (General build protection takes precedence over spawn protection)
+			if (!TShock.Config.DisableBuild || HasPermission(Permissions.antibuild))
+			{
+				// If they have spawn protect bypass, or it isn't spawn, or it isn't in spawn; continue
+				// (If they have spawn protect bypass, we don't care if it's spawn or not)
+				if (!TShock.Config.SpawnProtection || HasPermission(Permissions.editspawn) || !Utils.IsInSpawn(x, y))
+				{
+					// If they have build permission in this region, then they're allowed to continue
+					if (TShock.Regions.CanBuild(x, y, this))
+					{
+						return true;
+					}
+				}
+			}
+
+			// TODO: Implement warning system.
+
+			// If they lack build permission, they end up here.
+			// If they have build permission but lack the ability to edit spawn and it's spawn, they end up here.
+			// If they have build, it isn't spawn, or they can edit spawn, but they fail the region check, they end up here.
+			return false;
+		}
+
+		/// <summary>Determines if the player can paint on a given point. Checks general build permissions, then paint.</summary>
+		/// <param name="x">The x coordinate they want to paint at.</param>
+		/// <param name="y">The y coordinate they want to paint at.</param>
+		/// <returns>True if they can paint.</returns>
+		public bool HasPaintPermission(int x, int y)
+		{
+			return HasBuildPermission(x, y) || HasPermission(Permissions.canpaint);
+		}
+
 		/// <summary>
 		/// A list of points where ice tiles have been placed.
 		/// </summary>