Gui: Try to load Theme Parameters from file

This creates logic that tries to load user parameters from file as the
priority and pushes back older mechanism to lower layer. Older way of
loading theme parameters should be preserved until we release first 1.1
RC.

src/Gui/StyleParameters/ParameterManager.cpp

@@ -223,7 +223,17 @@ void UserParameterSource::remove(const std::string& name)
 
 YamlParameterSource::YamlParameterSource(const std::string& filePath, const Metadata& metadata)
     : ParameterSource(metadata)
-    , filePath(filePath)
+{
+    changeFilePath(filePath);
+}
+
+void YamlParameterSource::changeFilePath(const std::string& path)
+{
+    this->filePath = path;
+    reload();
+}
+
+void YamlParameterSource::reload()
 {
     QFile file(QString::fromStdString(filePath));
 
@@ -240,6 +250,7 @@ YamlParameterSource::YamlParameterSource(const std::string& filePath, const Meta
     std::string content = in.readAll().toStdString();
 
     YAML::Node root = YAML::Load(content);
+    parameters.clear();
     for (auto it = root.begin(); it != root.end(); ++it) {
         auto key = it->first.as<std::string>();
         auto value = it->second.as<std::string>();
@@ -288,7 +299,7 @@ void YamlParameterSource::flush()
 
     QFile file(QString::fromStdString(filePath));
     if (!file.open(QIODevice::WriteOnly | QIODevice::Truncate | QIODevice::Text)) {
-        FC_TRACE("StyleParameters: Unable to open file " << filePath);
+        FC_WARN("StyleParameters: Unable to open file " << filePath);
         return;
     }