core, eth, internal: Added `debug_getBadBlocks()` method (#3654)

* core,eth,internal: Added `debug_getBadBlocks()` method

When bad blocks are discovered, these are stored within geth.
An RPC-endpoint makes them availablewithin the `debug`
namespace. This feature makes it easier to discover network forks.

```

* core, api: go format + docs

* core/blockchain: Documentation, fix minor nitpick

* core: fix failing blockchain test

1 files changed, 6 insertions, 1 deletions

diff --git a/internal/web3ext/web3ext.go b/internal/web3ext/web3ext.go
index 2012c2517..e6bd18116 100644
--- a/internal/web3ext/web3ext.go
+++ b/internal/web3ext/web3ext.go
@@ -294,7 +294,12 @@ web3._extend({
 			call: 'debug_preimage',
 			params: 1,
 			inputFormatter: [null]
-		})
+		}),
+		new web3._extend.Method({
+			name: 'getBadBlocks',
+			call: 'debug_getBadBlocks',
+			params: 0,
+		}),
 	],
 	properties: []
 });