Support for fava option in accounts page

[prafullat]

Now account page supports fava options such as

show-accounts-with-zero-balance
show-accounts-with-zero-transactions

Fixes #1116

[yagebu]

This doesn't look quite right - it only checks if the account should be shown according to the total over all entries. I think it should instead check whether should_show is true for an account for all of the intervals.

[yagebu]

Closing this stale PR. Just reopen it if you ever want to continue this :)