Suggestion: On smartcoin explore page - add 'active smartcoin' filter?

On the [smartcoin explorer page](https://wallet.bitshares.org/#/explorer/assets) within the Bitshares wallet, the list includes smartcoins which are not currently active (perhaps due to a lack of price feed publishers), would it be possible to add a (by default ticked) filter checkbox to hide/show inactive smartcoins?

Hopefully this would draw more attention to the active smartcoins on the BTS DEX.

Start at the smartcoin explorer page linked in the issue and trace how the asset list is rendered and how inactive smartcoins are identified. Done means the page has a default-checked control that hides inactive smartcoins, can show them when unchecked, and keeps active smartcoins visible.

Written by the indexing model from the issue text.