Link to block hash rather than height

[jholdstock]

At present, every place where the GUI links to a block, it links to the height (eg. https://testnet.dcrdata.org/block/408322).

It should probably link to the hash instead (eg. https://testnet.dcrdata.org/block/0000003347c2a60b24c04e90bef7451db450f166110daedd9203d0c87e4a20c7).

It is possible multiple blocks could be found for the same height, so using the hash will remove the chance of linking to an incorrect block.

[davecgh]

Mind taking this on since I'm actively getting dcrpool updated now?