store current activity

add current activity to localstorage on activity start. reload it,
recalc duration on load.

remove prompt before reloading records, just do.

check for empty value when starting an activity, apply err class to
input if empty. entity '<' and '>' before using value.
move embedded styles to sheet. move embedded js to main.js

moved a few style rules out of markup, into stylesheet. removed main
app js from index.html added to main.js.