Adds ability to set the cell's accessoryType attribute.
Adds test for setting accessoryType.
Merge branch 'refs/heads/master' into pm2-accessory-type

* refs/heads/master:
  Fixes deprecation warning.
  Add long_press_action to the cell non-deprecated whitelist.
  Added migration guide to README
  Update README.md
  Version 2.0.0.rc1

Conflicts:
	lib/ProMotion/table/cell/table_view_cell_module.rb
Merge pull request #486 from clearsightstudio/pm2-accessory-type

PM2 table cell accessoryType functionality