Fixes #1654: Fixed the issue that a new message source object is generated for every new message being translated

fixed #1021

- added example code for application components
- added missing short description

[ci skip]

- refactored replaceNamedArguments.
- ensure gridview message works on all systems.

fixes #1072

issue #1072

Control statements based on the if and elseif constructs must have a single space before the opening parenthesis of the conditional and a single space after the closing parenthesis.

Fix declarations for yii\i18n\FallbackMessageFormatter::format() and yii\i18n\FallbackMessageFormatter::formatMessage()

they are not responsible for i18n ;)

[ci skip]

fixes #991

Removed intl version check since it's very inconsistent and it seems bundled versions are always the same ones for the same PHP versions

Fixes PHP 5.5 weird placeholder replacememt in case no arguments are provided at all (https://bugs.php.net/bug.php?id=65920).