Fix #193. Add short answers. Improve auto clicking of the Next button.

[glebkema]

Fix #193

Levels 19 and 24 have two solutions – with a shorthand property flex-flow and without it. When the user types a short solution, the Next button becomes available, but pressing Enter in the code area doesn't automatically activate this button.

To fix this, I've made the following improvements:

1. Add short alternatives for answers in the level.js file with the styleShort key.
2. Calculate the two data values min and max for the short and long versions of the answer (instead of the single parameter lines).
3. Check if the Next button is enabled to automatically click it (instead of comparing the length of the code).
4. Check if the code is longer than the short answer to start additional checks.
5. Check if the truncated code is longer than the long answer to prevent new blank lines from appearing.

I've tested the new behavior on my localhost.
Would be glad for your feedback.

[glebkema]

I've resolved the merge conflict for this PR