Update view plugin for 2.3
Update view plugin for 2.3

* The view plugin (as opposed to the _preview) will only work on
  CKAN>=2.3, so no need to handle both versions on the code. Fail if using
  CKAN<2.3.
* Simplified `can_view` logic for 2.3
* Removed all IPackageController stuff as it's no longer needed to
  create views by default

drnextgis/ckanext-geoview,pduchesne/ckanext-geoview,taijiang-tw/ckanext-geoview,singularita-corp/ckanext-geoview,kalxas/ckanext-geoview,smartlane/ckanext-geoview,pduchesne/ckanext-geoview,singularita-corp/ckanext-geoview,kalxas/ckanext-geoview,deniszgonjanin/ckanext-geoview,kalxas/ckanext-geoview,pduchesne/ckanext-geoview,bcgov/ckanext-geoview,taijiang-tw/ckanext-geoview,smartlane/ckanext-geoview,thobley/ckanext-geoview,drnextgis/ckanext-geoview,ckan/ckanext-geoview,bcgov/ckanext-geoview,thobley/ckanext-geoview,singularita-corp/ckanext-geoview,taijiang-tw/ckanext-geoview,drnextgis/ckanext-geoview,deniszgonjanin/ckanext-geoview,ckan/ckanext-geoview,deniszgonjanin/ckanext-geoview,smartlane/ckanext-geoview,ckan/ckanext-geoview,bcgov/ckanext-geoview,thobley/ckanext-geoview