modelStudio v0.2.0

• new plot: Target vs Feature [EDA] (#38)
• new plot: Average Target vs Feature [EDA] (#41)
• add boxplots to FI plot ingredients/72
• add new_observation_y argument to modelStudio (#39)
• pass ... to prepare_* functions (e.g. allows to round numbers)
• add margin_ytitle argument to modelStudioOptions
• by default: observations to calculate local explanations are taken at random from the data (#25)
• by default: first plot is selected as BD and second is clicked (#37)
• nicer histogram when few unique values
• all categorical plots now have the same bar order ingredients/82
• try_catch blocks added - errors in ingredients or iBreakDown functions are
  now treated as warnings and do not stop the modelStudio computation (#35)
• show_info adds messages saying what is currently calculated (#40)
• add spellcheck to tests (#36)
• Travis-CI now checks OSX