Allow Site Add While In Session

[xenotropic]

The program doesn't allow options to be edited while in a session, to "remove temptation". While it's a good idea not to allow sites to be removed during a session, adding a site to be blocked (the user just realized there is another temptation that needs to be blocked mid-session) would improve the extension in a way that is consistent with its purpose.

[matchu]

I think this is reasonable. Updating the UI is nontrivial (textboxes are just so simple! :P), but it might be a reasonable addition to the next major release.