Fixes #4184: mentioned a safer way of using dummy cache that works in case of merging configs of advanced app

Fix typo on elasticsearch readme file

Fixes #4051: Renamed `yii\caching\GroupDependency` to `TagDependency` and added support for associating multiple tags to a single cached data item

Remove extra import and fix comment

fixes #4301

Typos and errors in docs

Error in code example

Support for separating Read/Write Database

Improved global configuration of assetmanager

all fine now

closes #2427

Added `beforeCopy`, `afterCopy`, `forceCopy` properties to AssetManager

fixes #4209

Update input-file-upload.md

fix docs