explorer: Better Transaction Details

Better transaction details. The current version prints raw msgpack data of the transaction, this could be more readable. Some ideas:
* Formatted section for common transaction headers (sender, receiver, fee, type, first-valid, last-valid, signature)
* Custom formatting for each txn type:
* pay, asset, app, keyreg, etc
* Compute the txid
* Convert the sender / receiver from b64 encoded string to the Algorand formatted address string.
* Attempt to format the note using known common encodings (i.e. JSON, Text, Base64, Hex Viewer)