daqlite - multiple topics per detector

[mortenjc]

Enhance daqlite to suppport multiple topics per detector. We have chosen
to keep a contiguous pixel space so for each detector pixel ids are unambiguous.
This means that for detector N the first pixel will not be pixel 1 but be
1 + OFFSET(N)

Suggested solution:
add configuration option (OFFSET) which defines the start pixel id. The already existing
options will detrmine the number of pixels.

So for plotting we subtract the offset and discard any pixels outside the valid range.

This allows both the normal operation where only pixel ids from the expected range are present,
but also testing using only a single topic containing pixels from multiple detectors

[mortenjc]

believe this is done in another branch. Can reopen later.