Revert "added FileMailer implementation of mailer interface"

This reverts commit 7d6d01b4bc9d7a23a7f5ec2a145b60f4898c80d6.
Implemented file transport for mails.
Added display of installed extension to debug panel.
Added parameters to fileTransportCallback.
typo fix.
Adjusted extension list.
moved markdown dependency to required.
Fixes #1075: separated empty switch and empty display for ListView and GridView.
typo fix.
hide summary when empty.
fixed crud to work with table that has no PK but AR defines one
Fixes #1169: anchor doesn't work when enablePrettyUrl is false.
Fixes #1170
FIX: Relation names not mangled in \yii\db\ActiveQuery::normalizeRelations
More precise descripton fo Session::cookieParam
Changed important log messages to info level
Added log messages to user login and logout actions.
Fixes #1176.
Refactored Session as suggested in #1172
Fixed phpDocs [skip ci]