Rework google sheets and firebase as subsets of "Forwarder"

[mitra42]

SImilarities and differences between Firebase and Google Sheets forwarders.

Configuration

• period - how often to do periodic
• verbose - for debugging

Class methods

• setup - includes for example subscriptions if needed and starting timer
• periodic - done every xx seconds
• messageReceived(topic, value) - each time message received

Config read should create the forwarders
setup on main should loop through all forwarders
Periodic should be on a timer created by setup
messageReceived on main body should loop through all forwarders

[mitra42]

• Create base class Forwarder
• Google Sheets and Firebase subclass this
• Move any commonality down to subclass
• Maybe redo config so these are combined (probably not)
• COmbine Sheets and Firebases into single Forwarders Array (not yet)
  • Not trivial because if firebase is defined, collection is done before passing to
• Make sure specific, but different, functions of Firebase / Sheets called via array - some functions stubbed in Forwarder

Integration with server

• historyIntervalSeconds => intervalSeconds and push to server

LATER - other tasks

• Admin interface to add forwarders