add cancel button to 'my' offers, otherwise display 'fill' button

For "add cancel button to 'my' offers, otherwise display 'fill' button", I updated the offer text to be "Fill buy" and "Fill sell" (since I wasn't sure if that's what "Buy / Sell" meant... we can easily remove the "buy / sell".

The harder part was figuring out how to determine if an offer is "mine" or not on rendering. I reviewed the "agent.js" class, and I was able to add a method to figure this out by checking if the offer was from the user's wallet's address in "gui.js". That's how I "think" you can check if an offer is "my" or not.