remove unused 'img' asset type
remove 'asset' jsp taglib

this taglib element can be replace by assets with renderer set to false.
the term of 'asset' have been misuse in this situation.
fix tests who fail since the 'img' asset type was remove
Change in the Public API of AssetsRequestContext

- remove of hasScopes()
- change removeScopes() by excludeScopes()
- add getExcludedScopes()
- add a boolean 'withoutExcludedScopes' to getScopes() for retrieve scopes or scopes without excluded scopes

The 'AssetsTag' have also be impacted by this api changes.