CRM-13410 - CiviCase - Load XML files from extensions (as defined with hook_civicrm_caseTypes)

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* CRM-13410: Allow extensions to define case-types
  http://issues.civicrm.org/jira/browse/CRM-13410
CRM-13410 - Allow "Components" to define managed-entities

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* CRM-13410: Allow extensions to define case-types
  http://issues.civicrm.org/jira/browse/CRM-13410
CRM-13410 - CiviCase - Automatically register/unregister case-types defined via hook_civicrm_caseTypes

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* CRM-13410: Allow extensions to define case-types
  http://issues.civicrm.org/jira/browse/CRM-13410
Merge pull request #1653 from totten/master-case-type-ext

CRM-13410 - CiviCase - Add hook_civicrm_caseTypes