Added adding attachments to: assets & licenses

Many attachments (files) can be added to assets and licenses.
This can be done:
- for assets:
    - by "bulk actions" button on "assets search view"
    - by "add new one" button on "edit device view"
- for licenses:
    - by "add new one" button on "edit license view"
There is option for removing attachments in views:
- "edit device view",  "edit license view"