v0.6.0 Interactive pgtraj exploration - outcome of GSoC 2017

Final outcome of GSoC 2017.

Changed

• NEWS formatted according to Keep a Changelog
• sanitized tests that are now based on testthat
• as_pgtraj() -> asPgtraj() for consistent function names

Added

• explorePgtraj function and shiny application
• createShinyViews function that create two materialized views, all_burst_summary_shiny and step_geometry_shiny_<pgtraj>
• supporting functions for the two above in utils_shiny.R
• continuous integration services (Travis CI and AppVeyor)
• code coverage reporting
• vignette explorePgtraj
• section in README for explorePgtraj