allow for data transmission control by data volume rather than burst time

[sebkopf]

make it possible (preferable?) to go by transmission volume (eg 1024 bytes) rather than by time base spike with action option to "transmit" / "send" buffer. For settings, this would be typically sent together with a "save" and "send" request so settings are saved in EEPROM and then also the data is sent straight to the database.

[sebkopf]

will not implement this for now as it's primarily something we'd want for cellular based devices and they don't have enough FLASH memory at the moment to run substantive sdds particle devices anyways