Upgrade to expressive 2.0 and PSR-15 middlewares

[codeliner]

Would be nice to reflect latest changes in the PHP middleware area.

Migrate to expressive 2.0:

• https://framework.zend.com/blog/2017-03-07-expressive-2.html
• https://docs.zendframework.com/zend-expressive/reference/migration/to-v2/

Migrate middlewares to support PSR-15:

• https://github.com/php-fig/fig-standards/tree/master/proposed/http-middleware
• https://docs.zendframework.com/zend-expressive/reference/migration/to-v2/#http-interop

[codeliner]

If YOU want to work on the issue please drop me a note here!

[danizord]

@codeliner I can handle this one next weekend :)

[codeliner]

cool, thx @danizord

[codeliner]

@danizord any updates? @snapshotpl Might want to take this one, too? ;)

[snapshotpl]

@codeliner :+1:

[codeliner]

Closed by #44