Add a word counter

[xdmx]

I'm planning to use ownnote to write everyday at least 1-2 pages (instead of using 750words.com).

It'd be very useful to have a word count on notes so I know how much I've written each day and set a personal goal

[Fmstrat]

Added to the request list.

[ThomasDaheim]

In js/script.js, line 7: add "wordcount" to list of plugins should do the trick