Email components hierarchy created.
SwiftMailer applied as email solution.
Unit tests for \yii\email\swift have been improved.
Methods 'addText' and 'addHtml' added to \yii\email\BaseMessage.
'\yii\email\ViewResolver' added.
Email message render functionality added.
Email message interface extracted.
'ViewContext' interface extracted, files render workflow refactored to use this interface.
'ViewContext' renamed to 'ViewContextInterface'.
Merge branch 'master' of github.com:yiisoft/yii2 into email-swift-2
'email' renamed to 'mail'.
'SwiftMailer' recomposed into extension.
Vendor testing support provided.
'swiftmailer' extension unit tests fixed.
'MessageInterface::createAttachment()' renamed to 'MessageInterface::attachContentAsFile()'
Method 'MessageInterface::__toString()' added
BaseMailer::defaultMessageConfig published as BaseMailer::messageConfig
refactored message formatter
added unit test to verify AR afterSave isNewRecord value

closes #1084
ensure parameter types in baselistview message

fixes #1072
Merge branch 'master' into messageformatter-refactoring

* master:
  ensure parameter types in baselistview message
  added unit test to verify AR afterSave isNewRecord value
Merge branch 'master' of github.com:yiisoft/yii2 into email-swift-2
refactored MessageFormatter
fixed fallback message format parameter order
support integer number type in fallback message formatter