prodigenr 0.6.0

Major changes

• Removed abstract and poster templates. Abstracts are so small it isn't
  an important addition and (I sense) posters will for a while be created
  with other software tools (e.g. PowerPoint). Plus there aren't many
  mature and well-established poster packages in R at this point in time.
• Tidied up and trim down all the README files and include pointers to
  the prodigenr online documentation instead.
• Removed R script template files. Projects might be too diverse for
  these template scripts to make sense.
• Removed several dependencies, including the usethis package.
• Moved Git initialization setup out into new function called setup_with_git().