APC & SMES appearances. (#78)

* CEV-Eris SMES sprite as RSI.

Has been modified so that the light overlay states use alpha blending.

* Add tiny glow to SMES display sprite.

* Appearances work v2

* More WiP

* RoundToLevels works correctly on even level counts now.

* SMES -> Smes because MS guidelines.

* CEV-Eris APC sprite.

* APC visuals.

* Reduce SMES scale again to normal levels.

* Update submodule

Content.Shared/Utility/ContentHelpers.cs

@@ -0,0 +1,60 @@
+using System;
+
+namespace Content.Shared.Utility
+{
+    public static class ContentHelpers
+    {
+        /// <summary>
+        ///     Assigns the value <paramref name="actual" /> going from 0 to <paramref name="max" />
+        ///     such that it is divided into a set of (amount <paramref name="levels" />) "levels".
+        ///     Rounding is performed to the "middle" so that the highest and lowest levels are only assigned
+        ///     if <paramref name="actual" /> is exactly <paramref name="max" /> or 0.
+        /// </summary>
+        /// <example>
+        ///     Say you have a progress bar going from 0 -> 100 inclusive and you want to map this to 6 sprite states (0, 4 intermediates and full).
+        ///     This method allows you to easily map this progress bar to the sprite states.
+        /// </example>
+        /// <param name="levels">The amount of levels to subdivide into.</param>
+        /// <returns>An integer from 0 to <paramref name="levels" />-1.</returns>
+        /// <exception cref="ArgumentException">
+        ///     Thrown if levels is less than 1.
+        /// </exception>
+        public static int RoundToLevels(double actual, double max, int levels)
+        {
+            if (levels <= 0)
+            {
+                throw new ArgumentException("Levels must be greater than 0.", nameof(levels));
+            }
+            if (actual >= max)
+            {
+                return levels - 1;
+            }
+            if (actual <= 0)
+            {
+                return 0;
+            }
+            var toOne = actual / max;
+            double threshold;
+            if (levels % 2 == 0)
+            {
+                // Basically, if we have an even count of levels, there's no exact "mid point".
+                // Thus, I nominate the first one below the 50% mark.
+                threshold = ((levels / 2f) - 1) / (levels - 1);
+            }
+            else
+            {
+                threshold = 0.5f;
+            }
+
+            var preround = toOne * (levels - 1);
+            if (toOne <= threshold)
+            {
+                return (int)Math.Ceiling(preround);
+            }
+            else
+            {
+                return (int)Math.Floor(preround);
+            }
+        }
+    }
+}