Client side cron validation (add monitor)
Add missing help tooltips
Client side cron validation (edit monitor)

Also improved UI for parsley validation in add monitor.
Fix cron field regular expression

Note that the validation only checks that the characters are in the
valid range, but does not verify cron syntax. The server side will catch
syntax errors.
Fix overly restrictive content-type checks in graphite client

Resolves issue #3