Added note about logger component in bootstrap

fixes #4301
typo
phpdoc
Fixes broken app/link under non-Windows
Better Windows unlink as suggested by @cebe
Fixes #4310
Remove extra import and fix comment
Merge pull request #4311 from mickgeek/patch-2

Remove extra import and fix comment
Turned Cache::buildKey() into public [skip ci]
Fixes #4051: Renamed `yii\caching\GroupDependency` to `TagDependency` and added support for associating multiple tags to a single cached data item
Fix typo
Merge pull request #4323 from sebathi/master

Fix typo on elasticsearch readme file
Fixes #4184: mentioned a safer way of using dummy cache that works in case of merging configs of advanced app
Removed mentioning of DummyCache usage
Corrected app/link for Windows once again
Fixes #4324: removed old way of developing Yii from the docs since app/link is much better/simpler workflow
Fixes #4298: Renamed framework/messages/pt-PT to framework/messages/pt in order to allow fallbacks
avoid confusion about uploadRequired
Fixes #4297: Added check for DOM extension to requirements