Fix fatal errors in Petition signature flow and assign petition pageURL and title to Thank You and Social Networking templates

Testing "Sign Petition" flow in 4.2 found two fatal errors.

CRM_Campaign_Form_Petition_Signature::postProcess() - tag create api call returns "id" not "tag_id".
CRM_Campaign_BAO_Petition::checkSignature() - syntax error in sql

Also added assignment of petition title to Thankyou template, and passing title and petition URL to common/SocialNetwork.tpl so that the standard layout elements are present for petitions.