Add the ability to save the last known working URL via localStorage

[alexose]

This commit solves a little pet peeve of mine: If you're working on a device with a non- 192.168.4.1 IP address, you have to type it each time you load the REPL. Now, we can save the URL to localStorage, and replay it on load.

#hacktoberfest

[cwalther]

I’m curious, in how far is this not already solved by #16? I don’t have to type my IP addresses every time, because they are stored in my browser history / bookmarks.