Add replace_all()

This is just a function that will be used in the optimized tag-finding
function.

desktop_version/src/editor.cpp

@@ -86,6 +86,22 @@ bool compare_nocase (std::string first, std::string second)
         return false;
 }
 
+void replace_all(std::string& str, const std::string& from, const std::string& to)
+{
+    if (from.empty())
+    {
+        return;
+    }
+
+    size_t start_pos = 0;
+
+    while ((start_pos = str.find(from, start_pos)) != std::string::npos)
+    {
+        str.replace(start_pos, from.length(), to);
+        start_pos += to.length(); //In case `to` contains `from`, like replacing 'x' with 'yx'
+    }
+}
+
 void editorclass::getDirectoryData()
 {