Get dashboard by slug instead of UUID

(✿◠‿◠) Migration tried and tested with today's database!
(✿◕‿◕) Gives us nicer urls like `/edit/name-of-dashboard` rather than `/edit/302493248-uuidlol-32048732`
(/ ﾟ▽ﾟ)/ Slug is also a unique identifier
(っ◕ヮ◕)っ Avoids exposing uuid to end user

I prefer this way of looking things up because it's kind of human readable but at the same time works for the computer. UUIDs are still really useful for how we internally manage resources. For example we could potentially look up the history of a resource whose `slug` has changed multiple times, but the `UUID` will have remained the same.

###  ✧ʕ̢̣̣̣̣̩̩̩̩·͡˔·ོɁ̡̣̣̣̣̩̩̩̩✧ ✧ʕ̢̣̣̣̣̩̩̩̩·͡˔·ོɁ̡̣̣̣̣̩̩̩̩✧✧ʕ̢̣̣̣̣̩̩̩̩·͡˔·ོɁ̡̣̣̣̣̩̩̩̩✧✧ʕ̢̣̣̣̣̩̩̩̩·͡˔·ོɁ̡̣̣̣̣̩̩̩̩✧✧ʕ̢̣̣̣̣̩̩̩̩·͡˔·ོɁ̡̣̣̣̣̩̩̩̩✧✧ʕ̢̣̣̣̣̩̩̩̩·͡˔·ོɁ̡̣̣̣̣̩̩̩̩✧

![](http://38.media.tumblr.com/tumblr_llt9g2XXAv1qgijako1_500.jpg)