Update LSTM to use generator

[teubert]

Requirement Text
Update the LSTM model fit function to use a generator so the data doesn't have to be stored in memory

See Also
https://www.google.com/search?q=tensorflow+data+generator+keras+training+large+datasets&rlz=1C1CHBF_enUS880US880&oq=tensorflow+data+generator+keras+training+large+datasets&aqs=chrome..69i57j0i546l5.8190j0j4&sourceid=chrome&ie=UTF-8

DoD

• Implement feature