Unnecessary class "btn" removed.

This breaks the ability to add your own class and doesn't have any
usage.
Improved slugify() function.

Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Aenean commodo
ligula eget dolor.
Old:
lorem-ipsum-dolor-sit-amet-consectetuer-adipiscing-elit-aenean-commodo-ligula-eget-dolor
New:
lorem-ipsum-dolor-sit-amet-consectetuer-adipiscing-elit-aenean-commodo-ligula-eget-dolor

Weit hinten, hinter den Wortbergen, fern der Länder Vokalien und
Konsonantien leben die Blindtexte. Abgeschieden wohnen Sie in
Buchstabhausen an der Küste des Semantik, eines großen
Sprachozeans.
Old:
weit-hinten-hinter-den-wortbergen-fern-der-lander-vokalien-und-konsonantien-leben-die-blindtexte-abgeschieden-wohnen-sie-in-buchstabhausen-an-der-kuste-des-semantik-eines-groen-sprachozeans
New:
weit-hinten-hinter-den-wortbergen-fern-der-laender-vokalien-und-konsonantien-leben-die-blindtexte-abgeschieden-wohnen-sie-in-buchstabhausen-an-der-kueste-des-semantik-eines-grossen-sprachozeans

Skromny młodzieniec bo tak piękny i książki.
Old:
skromny-modzieniec-bo-tak-pikny-i-ksiki
New:
skromny-mlodzieniec-bo-tak-piekny-i-ksiazki

This--is-a-totally--weird-check!!!-believe-me-i'm-lying
Old:
this-is-a-totally-weird-check-believe-me-im-lying
New:
this-is-a-totally-weird-check-believe-me-i-m-lying

     Кюм эа ныморэ
факэтэ, диам чингюльищ дуо нэ.
Old: -
New:
kyum-ea-nymore-fakete-diam-chingyul-ish-duo-ne

     Υσυ εσε δοσθυς ιν.
Δετρασθο αντιωπαμ πρι συ, ομνις αυτεμ μαλυισετ ατ κυι.
Old: -
New:
ysy-ese-dos8ys-in-detras8o-antiwpam-pri-sy-omnis-aytem-malyiset-at-kyi

Déi wellen Fielse um, Fläiß d'Loft rëm jo.
Old:
dei-wellen-fielse-um-flai-dloft-rem-jo
New:
dei-wellen-fielse-um-flaeiss-d-loft-rem-jo
Slug generation optimized.
Optimized labels and added slug.js to edit.js.
Updated all labels.
Merge pull request #567 from FabianBeiner/0.9-dev

0.9 dev