ui: color schemes

Put all colors into single xml file. Accessing colors is handled via the singleton class ColorScheme. The default scheme
"bright.xml" holds the original colors. The scheme "dark.xml" is a start, but still a poor alternative. Color schemes
can be switched via the View menu.

src/lib/Application.cpp

@@ -11,6 +11,7 @@
 #include "component/view/ViewFactory.h"
 #include "data/StorageCache.h"
 #include "settings/ApplicationSettings.h"
+#include "settings/ColorScheme.h"
 
 std::shared_ptr<Application> Application::create(ViewFactory* viewFactory)
 {
@@ -32,6 +33,8 @@ std::shared_ptr<Application> Application::create(ViewFactory* viewFactory)
 void Application::loadSettings()
 {
 	ApplicationSettings::getInstance()->load("data/ApplicationSettings.xml");
+	ColorScheme::getInstance()->load(ApplicationSettings::getInstance()->getColorSchemePath());
+
 	GraphViewStyle::loadStyleSettings();
 }