implementation of the slideshare widget
pull request feedback

+ thumbnail.html.haml is automatically generated by the widget api
  generator
+ add changelog entry
+ add integration test entry
+ usage exceeded 80 characters
+ hash keys were not in consistent ruby 1.9 style
+ use dashes in css class instead of underlines
+ leave "text-center" out as it is not needed and depends on design
+ don't use rescue to catch all exceptions (leads to hard to maintain
  code, swallows errors from sub methods and has a bad performance)
+ pass in variables to private methods instead of using class wide data
  directly to make those methods more independent and simpler to
  understand
+ rename methods to reflect the purpose not the implementation
Merge branch 'develop' into feature/slideshare

* develop:
  bugfix: slider used headline attribute on link instead of title

Conflicts:
	CHANGELOG.md
Merge branch 'feature/slideshare' into develop

* feature/slideshare:
  pull request feedback
  implementation of the slideshare widget