CRM-15578 - Add crmMailingMgr.mergeInto()

This should be useful for creating different variations on a mailings in A/B
testing.
CRM-15578 - Add crmMailingAB2 module (based on crmMailingAB). Add skeletal list/edit screens.
CRM_Mailing_Info - Fix warning
attachments.html - Remove one level of indirection
crmMailing2 - Autoformat
CRM-15578 - crmUiSelect - Update to work with ngModel
CRM-15578 - Refactor crmUiField

This splits crmUiField into a few smaller pieces: crmUiField, crmUiId,
crmUiIdScope, crmUiFor.  This loosens the coupling and also makes it easier
to create reusable components which combine them.
CRM-15578 - crmMailing2 - Extract misc, simple directives

<div crm-mailing-block-header-footer crm-mailing="mailing"/>
<div crm-mailing-block-mailing crm-mailing="mailing"/>
<div crm-mailing-block-preview crm-mailing="mailing"/>
<div crm-mailing-block-publication crm-mailing="mailing"/>
<div crm-mailing-block-responses crm-mailing="mailing"/>
<div crm-mailing-block-review crm-mailing="mailing"/>
<div crm-mailing-block-schedule crm-mailing="mailing"/>
<div crm-mailing-block-summary crm-mailing="mailing"/>
<div crm-mailing-block-tracking crm-mailing="mailing"/>
<div crm-mailing-body-html crm-mailing="mailing" />
<div crm-mailing-body-text crm-mailing="mailing" />
CRM-15578 - crmAttachments - Convert include+ctrl to a directive
CRM-15578 - crmMailingAB2 - Add testing_criteria_id
CRM-15578 - MsgTemplateCtrl - Don't hardcode dependence on upstream "scope.mailing"
CRM-15578 - crmMailing2 - Fix regression in "From Address".

Also: Make convention compatible with editing multiple mailings.
CRM-15578 - crmUiWizard - Allow conditional steps
CRM-15578 - crmMailingAB2 - Implement joint composition screen (for "Subject" and "From" testing)
CRM-15578 - crmMailingAB2 - Support for attachments
CrmAttachment - Fix bug wherein multiple CrmAttachments mix up their targets.
CRM-15578 - crmMailingAB2 - Make crmMailingAbBlockMailing more consistent+flexible
CRM-15578 - body_text, body_html - Allow multiple instances

This commit removes the previous crmUiId() service and makes consistent use
of the newer, more adaptible crmUiId and crmUiIdScope directives.
CRM-15578 - crmMailingAB2 - Implement separate composition screens
CRM-15578 - Implement crmMailingAbSlider