Make the ChainInformation builder support older runtimes

[tomaka]

At the moment, the ChainInformation builder assumes that the runtime contains some functions.
If not there, it will simply fail.

Unfortunately, some of these functions have been added after the launch of Polkadot, and are not available in earlier versions.

It should, however, be possible to simply query the elements from the chain storage.

[tomaka]

It turns out that the Babe next epoch information isn't available in storage. We added a storage entry at the same time as BabeApi_next_epoch has been added.

[tomaka]

Closing as not doable.