LPD Mini component needs changes

[takluyver]

We added the LPD mini detector in #370, thinking it was a straightforward 256 x 256 pixel detector, like one LPD-1M supermodule. We've now found it's a variable number of 64 x 128 modules. FXE will have 3 modules, one of a different type, so we expect 1 or 2 modules to make up a 'detector'.

Each module is read out as a 32 x 256 stripe of a 256 x 256 'frame' (the hardware can have up to 8 modules). To present a nice API, we'll need to figure out how this will appear in the raw & proc data. Currently, the raw data just saves the whole 256 x 256 frame, but this is wasteful since most of it is garbage. If we can't cut out the excess before saving it, we'll probably do so in offline calibration.

cc @cydanil @philsmt