Grand Exchange Plugin redesign

General:
- Applied the design I proposed in issue #1342
- Applied custom component: MaterialTabs
- Removed default scrolling behaviour from parent PluginPanel
- Added error panels for empty searches and empty offer slots
- Added new formatter to the StackFormatter that displays integers
as rs stacks with decimals (21700 into 21.7k)
- Changed the Locale on the stack formatter and respective unit testing
to UK, this makes sure all tests are consistent with Travis (ex: i ran
the unit testing in europe, travis ran in the us, so it passed my tests,
failed his)

Offers:
- Refactored the GE offers into it's own seperate file:
GrandExchangeOffersPanel
- Redesigned the ge offers items
- Included the custom component ThinProgressBar on the bottom of each
ge item panel
- Added secondary information panel, toggled by clicking on the primary
panel
- Added a game state check that resets all ge offers on logout

Search:
- Recoloured and resized the search bar
- Added new icons to the search bar (incluing a loading wheel gif)
- Removed focus on the search bar when results are displayed
- Added custom scrolling behaviour
- Blocked input when search is in progress

runelite-client/src/main/java/net/runelite/client/util/SwingUtil.java

@@ -94,6 +94,14 @@ public class SwingUtil
 		System.setProperty("sun.awt.noerasebackground", "true");
 	}
 
+	/**
+	 * Converts a given color to it's hexidecimal equivalent.
+	 */
+	public static String toHexColor(Color color)
+	{
+		return "#" + Integer.toHexString(color.getRGB()).substring(2);
+	}
+
 	/**
 	 * Safely sets Swing theme
 	 *