t/devices.html: Auto configuration for common devices

[Trek Hopton]

A great feature to have would be a configuration option on the device page that prefills a number of commonly used variables. Eg. Variable defaults for ESP when an ESP is being registered.

These can be found in AusOcean documentation here:

https://docs.google.com/document/d/1xdS0qk25hFhkAivB2wlzd5U0ZxGEyk_avg-NGPYXtc4/edit#heading=h.v5ujelh40ici

This would also be useful for camera variables, hydrophone variables, speaker variables etc.

For each device type we could have a default variable list that can be added at the click of a button.

[Alan Noble]

This could be implemented by extending the /vars method, which is how devices indicate the variables they support and their types.

For example,

{"PulseWidth":"uint"}

could be extended

{"PulseWidth":"uint,50"}

This would signify that the PulseWidth variable is an unsigned integer with a default value of 50.

Further, default values would default to their typical default values.

For example,

{"AlarmPin":"uint"}

would indicate the AlarmPin defaults to zero (the current situation).