HOCON tests

Suite of tests for HOCON lexer, parser and formatter along with some cosmetic corrections in the codebase.

I had to add `intellij-hocon` module as a dependency to `SBT` module. Without this, tests won't run because scala plugin descriptor is incorrect when it cannot see HOCON subdescriptor. This applies to all tests, not just HOCON tests.

I tried to write tests based on how similar Scala tests were implemented. Implementation of formatter test suite was a little modified to allow embedding custom code style settings as an XML in the `testdata` files.