[alias-server] Organizing files into src folder

Summary:
T3060

In building the old stack, recognized it was much better to have node files in an src folder, with a single index.js at the top level along with admin config files. Adopting this structure early on.

Test Plan:
Confirm config.js import is adjusted on all files in new src/ folder
wipe database and node index.js, app will run and error out trying to send too many tg msgs

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D13511