Transfer to .cpp
Add data interpolation
Add test
Discover that dp is not correctly interpolated
Disable test before commit

This allows the processor to get configured according to some sensor
params.

Implemented with Processor::setup(), but can also work directly with the
Processor constructor.

feature imu
capture imu
feature corner 2d
lmk corner 2d
processor imu
sensor imu

...by setting constant Jacobian parts in the constructor.
Also, start making many functions void and use data members instead