In the case where external items are used with the context extension,
features are paged during fetch time. Therefore the number of items in
the 'items' collection is always less than the item page limit, so
it's necessary for the Vue table based paging to always 'stay' on page
1 to show the current item list.

This is useful if you want to test stac-browser against a STAC that
does not have the CORS permission to be used in stac-browser.

For example, with http-server installed from npm nad running

```
http-server -p 1111 --proxy https://geobase-spot-dev.s3.amazonaws.com/
--cors
```

to proxy the geobase STAC, and then running stac-browser with

```
CATALOG_URL=https://geobase-spot-dev.s3.amazonaws.com/catalog.json \
           STAC_PROXY_URL="https://geobase-spot-dev.s3.amazonaws.com|http://localhost:1111" \
           npm start
```

Allows for proper browsing of that STAC.

This updates the collection extent format to the 0.8 and above
specification. This also accounts for backwards compatibility, so
pre-0.8 STACs will still work.

This commit deletes the "dictionary.json" property map that exists,
and creates a `property.js` file that defines mappings between
property names and display information for use in the property bar. It
also adds properties and extenions for 1.0.0-beta.1.

This commit adds async schema validation that fetches schema based on
the stac version of the object being presented.