Don't assign `major_actions` it is overwritten later.
Also display `pdf-tasks-listing` and `task-report` for inbox task-listings.

Closes #535.
Merge pull request #575 from 4teamwork/deif-add-inbox-actions

Also display `pdf-tasks-listing` and `task-report` actions for inbox task-listings.
Moved DictStorageConfigurationContext to opengever.base.
Added option to disable download confirmation.
Catch up with latest changes on master, minor refactoring.
Add simple key-value store api.
Display portal message instead of 404 when attempting to download missing file.