CRM-15145 - additional styling for upgrade message, change register link in install success message, update CONTRIBUTORS.txt.

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* CRM-15145:
  https://issues.civicrm.org/jira/browse/CRM-15145
Merge pull request #3959 from davecivicrm/CRM-15145a

CRM-15145 - additional styling for upgrade message, change register link...