Move script to a separate file.

Unable to take advantage of my editor otherwise.
Also one can link to the separate script from userscript definition,
allowing for easier development.
Clean up some JavaScript quirks.

- Turn on strict mode.
- Add missing semicolon.
- Eliminate check for minutes != 0 (dividing 0 is a safe operation).
- Eliminate unused `result` variable.
- Remove array initialization, it's never used.
- Replace !=null test with simple truthyness check.

Mostly because I'm customed to running JSHint while development
to report me of possible problems, but it's of no use when the
whole code shows up underlined.
Rename accum() to parseToMinutes() to aid my understanding.

Also just check for the truthyness of `time`.
Write the sum into new row in footer.
Calculate both of the estimate columns.