[Feature request] Client-side tx checking
The "decode outputs" / "prove sending" tools are very useful as they allow users to conveniently check if their transactions have been processed as intended. However, in the current implementation, the user's secret key (the view secret key or the tx secret key) is sent to the server in order to perform the check on the server side, which is quite undesirable because a malicious entity running the explorer could keep record of all the submitted secret keys and abuse the knowledge.

Giving out one's view secret key is particularly problematic, as it alone enables guessing outgoing transactions of that particular wallet quite accurately, as I explained here:

- https://www.reddit.com/r/Monero/comments/7plvvd/monero_observer_new_issue_jan_2_8_weekly_monero/dsiak2l/

(The very tool in the above explanation is provided by this explorer.)

It'd be much more desirable if this check could be performed purely client side, similar to @luigi1111's implementation in JavaScript:

- https://xmr.llcoins.net/checktx.html

Could you please consider integrating the above code into the explorer, so that the above security risk can be circumvented?

Thank you!
