More choices for opcode.txt tool

[x87]

I'm a big fan of the Make opcode.txt tool but, my experience as a new user was similar to:

"Hm... Wonder what this does."

"Sure, why not?" then, "Where'd my file go?" and later. "What's this do?"

Because I had a SaveAnywhere script open for Make opcode.txt.

Locking this power tool when not in admin mode seems a bit extreme. Most users won't ever need to use this tool. A lot more warning seems warranted.

Maybe change the first dialog to Open (in Sanny), Save As (working directory), Overwrite, or Cancel, And then throw a clarified warning if Overwrite is selected.

Originally posted by @OrionSR in #16 (comment)

[x87]

As of 4.1 opcodes list is generated automatically from JSON, Make opcodes.txt is no longer part of SB