UI: Fixed case to match what the files are named

The files on disk are lower-case but QSS refrences them in
upper-case. Windows doesn't report errors as the platform isn't case
sensitive. Error messages are generated and icons not to render on
case sensitive platforms such as Linux and Mac

UI/data/themes/Acri.qss

@@ -155,8 +155,8 @@ QListWidget QLineEdit {
 
 /* Dock stuff */
 QDockWidget {
-	titlebar-close-icon: url('./Dark/Close.svg');
-	titlebar-normal-icon: url('./Dark/Popout.svg');
+	titlebar-close-icon: url('./Dark/close.svg');
+	titlebar-normal-icon: url('./Dark/popout.svg');
 }
 
 QDockWidget {

UI/data/themes/Dark.qss

@@ -120,8 +120,8 @@ SourceTree QLineEdit {
 /* Dock Widget */
 
 QDockWidget {
-	titlebar-close-icon: url('./Dark/Close.svg');
-	titlebar-normal-icon: url('./Dark/Popout.svg');
+	titlebar-close-icon: url('./Dark/close.svg');
+	titlebar-normal-icon: url('./Dark/popout.svg');
 }
 
 QDockWidget::title {

UI/data/themes/Rachni.qss

@@ -189,8 +189,8 @@ QListWidget::item:hover:!active {
 /***********************/
 
 QDockWidget {
-	titlebar-close-icon: url('./Dark/Close.svg');
-	titlebar-normal-icon: url('./Dark/Popout.svg');
+	titlebar-close-icon: url('./Dark/close.svg');
+	titlebar-normal-icon: url('./Dark/popout.svg');
 }
 
 QDockWidget {