Fix #235 allow remark in prod with a limit on extrinsic size for free...

Fix #235 allow remark in prod with a limit on extrinsic size for free transaction (!278)

* add fees consts

* allow remark with event

* fix filter

* fix fees for small length

* update documentation

* adjust length fees

* refactore fee tests

* add extrinsic length limit

* authorize remarks