Revert "Only invoke jscolor if browser does not support HTML5 color element."

This reverts commit 94c88795279b57b32e5909119f20fc2030f67238.
Fix color field usage.

Drop use of HTML5 color fields, since they are too limited: only accept
RGB specifications and do not allow for empty fields. Make sure jscolor
is included where required and not where not. Do not repeat w3schools
link on every row of table of problems in a contest.