Some debug code style fixes, and https://github.com/yiisoft/yii2/issues/1478#issuecomment-31446267 fix
Merge pull request #1751 from lucianobaraglia/some-debug-fixes

Some debug code style fixes...
Removed unnecessary text
migration guide improved
Merge pull request #1753 from Ragazzo/migrations_docs

migration guide improved
add handler property to yii\web\Session
Added to the basic app, fixed config, added to core commands.
fixture controller improved
added .travis.yml to basic app

issue #1744
Reverted config change

change was made in 0d263a12a9dbf3f0cb8569db40f0581dc002285b

issue #1744
alias fixed
Merge pull request #1759 from Ragazzo/fixtures_controller_improvements

Added to the basic app, fixed config, added to core commands.
Basic app: DB configuration in separated file
code style fixes
moved dev requirements to require-dev in app composer.json

fixes #1736
Merge pull request #1761 from lucianobaraglia/master

Basic app: DB configuration in separated file
simpler implementation of the handler property in yii\web\Session
CHANGELOG maintainance and code style
applied fixture command docs from #1762

closes #1762
Changed elasticsearch AR primary key handling

now supports mapped primary key when _id is part of source with an
alias.