[REST] make selection of output-format mandatory, support dot url syntax
[REST] make selection of output-format mandatory, support dot url syntax

1. Remove the default format (binary) because `rest/block/<hash>/Hex` would end up delivering binary data.
2. List available formats when chosen format was not found (reduces need for documentation)
3. Change url syntax to dot extension like format chosing (like `rest/tx/<hash>.json`

(cherry picked from commit 8a5c9513ba24c2cb0e0889474e32f108a29d087b)

reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin