Load/Save SFG to file

Description of issue:

Implement the ability to save an SFG to a file. Also implement the ability to load the SFG from a file. This is mainly going to be used by the GUI, however it should work on the text interface as well.

Linked Requirements:

( None )

Potential Issues:

None

Blockers:

( None )

Issue Requirements:

1. A SFG should be able to be saved to a file by the user.
2. The user should be able to save to a file of their choosing. Note: not a type of their choosing just a filename.
3. The user should be able to load a SFG from a file.

Comment:

There is no specific requirement on how to this save/load needs to work other than that the SFG should not be modified while saving/loading.