Bump sbt from 0.13.2 to 0.13.6

Conflicts:
	project/build.scala
Add Travis CI settings
Bumped minor versions of libraryDependencies, add dependencyOverrides for scala-lang deps

Conflicts:
	project/build.scala
Fix some TODO in build settings

 - Remove ls-sbt (https://github.com/scalatra/scalatra/pull/423 )
 - Note about scalaz-7.0.x compatibility (https://github.com/scalatra/scalatra/pull/425)
 - Back to Scala 2.11.2 for now

Conflicts:
	project/build.scala
Merge pull request #427 from seratch/feature/from-2.3.x

Merge @seratch's four PRs on build settings into 2.4.x branch