Move included_applications to applications in .app.src

Usage of included_applications is evil as it potentially breaks stuff for any
other applications using syntax_tools or goldrush[1].

Also use `lager:start()` instead of `application:start(lager)` in test setup
for ensuring deps (goldrush) are started.

[1]: http://learnyousomeerlang.com/the-count-of-applications#included-applications