create submodules for ecc and aionostr

[ecdsa]

The ecc submodule is there twice:

• electrum/ecc
• electrum/aionostr/ecc

The install script copies libsecp256k1.so.2 in only one of them.
That seems to be enough, because of the way loadLibrary works.
However, we might forget about that. Should we copy it twice instead?`

[ecdsa]

aionostr uses the websockets package.
apparently, that package does not work with a proxy.
https://stackoverflow.com/questions/47225488/client-websocket-connect-through-proxy
maybe we could use websocket-client instead.

[accumulator]

The ecc submodule is there twice:

* electrum/ecc

* electrum/aionostr/ecc

The submodule paths could be added to the python interpreter search path, similar to what is done in run_electrum:

if is_local or is_android:
    sys.path.insert(0, os.path.join(script_dir, 'packages'))

There should be no need for a copy in electrum/aionostr/ecc.