Add social plugins to Event, Donation and tell a friend page

Ability to add the social networking plugins on civicrm pages ( facebook like, tweet and +1 )
Note: Petition has this feature so you should check and generalize it.

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Database changes
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• add "is_share" tinyint(4) in civicrm_event
• add "is_share" tinyint(4) in civicrm_contribution_page

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Functionality
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For Events

• For new event page, add a checkbox "Enable Sharing?" below Public Event
• If sharing is enabled then show sharing links on Event Info page, thank you page, email receipt and tell a friend page

For Contributions

• For new contribution page, add a checkbox "Enable Sharing?" above is active
• If sharing is enabled then show sharing links on Contribution page, thank you page, email receipt and tell a friend page

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Upgrade
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• schema upgrade
• message template upgrade