Add emoji-clock plugin

which displays the current time with half hour accuracy as an emoji
symbol, for example in the shell prompt.
"$PWD" = "PWD", >! doesn't work, echo is redundant. Fixed all.
Merge pull request #1689 from afh/pull/emoji_clock

Add emoji-clock plugin
Merge pull request #1699 from Bercio/patch-1

>! doesn't work with noclobber. changed >! to >| and  echo "$PWD" to pwd(redundant)