Fixes device sequence loading & editing of devices by sequence

Fixes issue reported in: twilio/OpenVBX#224

Fixed device order return in model for search, get_by_user.
Added 'sequence' to add function where it specifies fields to save.
Also fixed devices.js to send sequence based on device list presence and state.

I'm not sure what VBX_Device::get_by_group is used for, but those SQL options will probably need to change too, at line 117. I can fix this if someone can point me towards a use-case. But...I couldn't find VBX_Device::get_by_group in use in core.