Point to correct theme, and some cleanup

src/source.cc

@@ -61,7 +61,7 @@ file_path(file_path), project_path(project_path) {
   auto style_scheme_manager=Gsv::StyleSchemeManager::get_default();
   style_scheme_manager->prepend_search_path(Singleton::style_dir());
 
-  auto scheme = style_scheme_manager->get_scheme(Singleton::Config::source()->theme);
+  auto scheme = style_scheme_manager->get_scheme(Singleton::Config::theme()->theme);
 
   if(scheme) {
     get_source_buffer()->set_style_scheme(scheme);

src/source.h

@@ -22,7 +22,7 @@ namespace Source {
   public:
     unsigned tab_size;
     bool show_line_numbers, highlight_current_line;
-    std::string tab, background, background_selected, background_tooltips, font, theme;
+    std::string tab;
     char tab_char=' ';
     std::unordered_map<std::string, std::string> tags, types;
   };  // class Config