I just took a look at it. The base is there but in order to really make it as good as it could be here a are few sugestions.
1. Use the common Dialog for saving and loading its pretty easy to use if you need help ask around.
2. make the Save button an add Key button having both a save and save file is confusing.
3. Why is the name of the key shown but not the value?
4. In the about, the web address is scirra.com not .net
Good for a first release and these changes will help a lot. What are you planning on using this for or is it just a little learning thing?