Replace receiver files suffixes for the corresponding tesnet subfolder path

[DevElCuy]

Devcoin 22.x has a working but outdated implementation for receiver files. Priorities to fix here:

1. Tesnet, Regtest and Sigtest have their own subfolders within data directory (i.e: .devcoin/ in Linux), receiver files should be downloaded into the respective subfolder
2. Suffixes for receiver files aren't working, we should remove that code in favor of the above.

We need #79 for working on testnet and sigtest. For regtest things are different, we need harcoded receiver files rather than downloading anything, since regtest is intended for working locally (networking should not be required).