A lot of changes

Remove unused constructor of messages::Message
Fixed LimitedQueueSnapshot _-prefixes
Changed LimitedQueueSnapshot's usage of int to std::size_t
ColorScheme is no longer a singleton
Created a "BaseWidget" class which is pretty much a QWidget except it
has a reference of ColorScheme since most widgets will need a reference
to the style they should use.
BaseWidget can be implemented either with a BaseWidget parent (which
will copy the ColorScheme reference from the parent) or with a
normal QWidget parent and an explicit ColorScheme reference.
Save main window geometry on close
Fix font changing in the Settings Dialog
Update settings library version

src/fontmanager.cpp

@@ -9,10 +9,10 @@ FontManager::FontManager()
     , currentFontSize("/appearance/currentFontSize", 14)
     , currentFont(this->currentFontFamily.getValue().c_str(), currentFontSize.getValue())
 {
-    this->currentFontFamily.valueChanged.connect([this](const std::string &newValue) {
+    this->currentFontFamily.getValueChangedSignal().connect([this](const std::string &newValue) {
         this->currentFont.setFamily(newValue.c_str());  //
     });
-    this->currentFontSize.valueChanged.connect([this](const int &newValue) {
+    this->currentFontSize.getValueChangedSignal().connect([this](const int &newValue) {
         this->currentFont.setSize(newValue);  //
     });
 }