Language selection guidelines

https://wikia-inc.atlassian.net/browse/AR-18

The question of which languages do we support and what is the criteria for evaluating new languages has come up several times. This is an attempt to create a guideline that covers these topics and guide the decision making process.

/cc @pchojnacki @nmonterroso 
@drsnyder 
small note regarding Scala. Almost all of DataAPI went through coursera Scala course, so there is some 'expertise' the rest of scala is mostly JVM anyway. We just hadn't had opportunity to write new services in it.

Also pretty recently I worked with Spring Java stack (Holmes) and I would certainly suggest to team to write our next JVM projects in something different, preferably Scala.

Small note on Scala vs Clojure. Not everyone likes Lisps :). And Play/Akka is very powerful toolset. 
Also there are 16k articles about Clojure on SO, and more than 30k about Scala. + there are quite few companies in and around Poznan that have people using scala. 

Anyway I think since its all JVM anyway, it doesn't make much difference in regards to Logging, deployment etc.