Audit dcrtime results against dcrdata

[fernandoabolafio]

In order to increase the reliability of the timestamp results, the app needs to audit the anchored results in dcrtime by:

• Check that the digest of a given result is in the provided merkle path.
• Check that the merkle path leads to the provided merkle root.
• Check that the merkle root is in the provided transaction.

[tiagoalvesdulce]

We can add a section that works pretty much the same as the dcrtime_checker CLI in the future. This way a user will be able to verify directly against the blockchain. Keeping this issue open until this is implemented.

Quoting Dave on matrix:

A proof file consists of a digest to prove, the merkle root, the leaves of hashes needed to provide that digest is actually covered by the merkle root, and some other things.
When you drop a non-proof file, the only thing you have available is the hash of the file, so it goes and does a database lookup. The functionality is convenient, and should definitely stay. It works well for the service itself.
However, when it comes to actually proving a hash is timestamped with a proof file, that functionality is missing from the GUI.

Depends on decred/dcrtime#89