bug: better resolution on fetch errors

[SgtPooki]

When fetching content that can't be found, you have to reload the page. This shouldn't be required.

from @aschmahmann:

• Once you start loading the eth blocks you can’t load anything else until you refresh
  • Likely true for any other “stressed” lookup which overtime causes sluggishness + hanging
  • Same with what happens if you try and load a block that isn’t discoverable, it eats up all the resources

NOTE: eth codec and blocks were removed, but problem is related to the page not rendering some fallback view when fetch fails. It should instead stop all node fetching and present user with "Okay, take me back to start exploring page" or similar.