Using collect instead of the static map

`STATIC_MAP` is no more, what does it change?

1. the files MUST be copied (or symlinked) into the `instance_path` folder.

    ```console
    # copy
    $ inveniomanage collect
    # symlink
    $ inveniomanage config set COLLECT_STORAGE invenio.ext.collect.storage.link
    $ inveniomanage collect
    ```
2. no files SHOULD be served from the package itself. (`send_static_file` is no more)
3. you can relate to other files by using direct paths, e.g. in less `@import "../less/bootstrap/bootstrap.less"`