Todo: Store icons in the settings via index instead of strings

This allows us to use something else than a string in order to reference
icons. For an upcoming patch this will be necessary.

Since this patch introduces a settings structure change, a migration
feature from the old "Keyword\iconResource" string to the new "Keyword
\iconType" int is implemented.

Change-Id: Ia5695418fb135510ed549cf9a7cb59aab5389f31
Reviewed-by: Alessandro Portale <alessandro.portale@theqtcompany.com>

src/plugins/todo/keyword.cpp

@@ -31,6 +31,9 @@
 
 #include "keyword.h"
 
+#include <coreplugin/coreconstants.h>
+#include <utils/themehelper.h>
+
 namespace Todo {
 namespace Internal {
 
@@ -41,7 +44,7 @@ Keyword::Keyword() : color(Qt::white)
 bool Keyword::equals(const Keyword &other) const
 {
     return (this->name == other.name)
-        && (this->iconResource == other.iconResource)
+        && (this->iconType == other.iconType)
         && (this->color == other.color);
 }