typo

Incomplete obsolete filling in i18n db extractor

Obsolete keys searching isn't work when we have serveral categories for tranlation with DbMessageSource. Obsolete array filled with last message category only, because it'll always overwritten.

Fix for #2020: docs about cross-DBMS relations

Fix #3429: Incorrect path to AppAssets at docs

verify issue #3473

Adding rotateByCopy to yii\log\FileTarget #3562

Looks good!

Question: Not sure about the point being made with components and
DatePicker. Please clarify if I misinterpreted.

fixes #2797

Fixes #3542: Removed requirement to specify `extensions` in application config

Conflicts:
	framework/CHANGELOG.md

[Travis CI] Include nightly HHVM builds into the build matrix

fixes #3578