Revive block explorer

[rpanic]

Currently the old block explorer has vanished from the main branch mysteriously.
In the future however, we want a modular and reusable block explorer for protokit.

We can either:

• Revive the old block explorer, update it and expand it with the new features
  See 09a32f7
• Revive one of the block explorer developed during previous hackathons by community members
  https://github.com/satyambnsal/ProtoScope
• Start from scratch