Major refactor

This branch refactors the majority of main.py out into individual
modules to compartmentalize the code.  Migrated all email related
features unti email.py, sending of messages into messaging.py

Also refactored all of the socket code to use aprslib for all APRS-IS
communication as well as message/packet processing.

Moved the email command into it's own Plugin.

.github/workflows/python.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [2.7, 3.6, 3.7, 3.8, 3.9]
+        python-version: [3.6, 3.7, 3.8, 3.9]
     steps:
     - uses: actions/checkout@v2
     - name: Set up Python ${{ matrix.python-version }}