Adding Google Analytics and Social Tracking support.

Removed legacy display types.
  AddThis module contained some small non generic display types. They where
  removed in favor of the display types added in the addthis_displays submodule.

Redesigned the config page.
  The settings page has been made more condensed and options have been merged
  into clear categories. There are some options that where removed because of
  legacy functionality that is now support inside the display types.

- Minor updates to README.txt

- Using field formatters to select the sharing widget type in the UI (contributed by Matthias Glastra, matglas86, http://drupal.org/user/573464)

- Decided not to use instance level settings as having one type of sharing widget per entity instance type is more logical in most cases
  - There might be some special cases where you actually need to have a different type of widget for entities of the same type, but currently we try to keep this as simple as possible

Moved AddThis configuration generation to a separate class. Replaced some NULL-checks with empty-call where appropriate. Enabled co-brand message configuration.

- Added tests
- Added some check_plain()-calls

- Refactoring and renaming

- Renamed AddThis username to profile ID, as this is more consistent with the current API described at addthis.com
- Moved some literals to AddThis-class as constants to reduce literal duplication

- Moved AddThis username configuration under Configuration / System / AddThis (previously under field settings)
- Changed widget type selection to use 'select' instead of 'radios'
- Added tests