check for changes to Account form before allowing the user to navigate away; add cancel button

[alanb2718]

If you make an edit on the Account form, you can navigate away from that tab and lose the changes. There should also be a cancel button to abandon the edits.

[pjaudiomv]

part of this could be difficult because of router ItalyPaleAle/svelte-spa-router#288. cancel button would be easy