Fix MM Digitization Warnings

This MR is to reduce the number of warnings created during the MM digitization due to the creation of invalid digits. All the strips in the active volume now return a channelNumber and position, even the pcb gap strips. Added a function to get the first and last active MM strip. Updated the MM strip response code to only digitize the read-out strips. The dead strips are still used in the strip physics simulation but are simply not digitized in the end (including pcb gap strips). Fixed some indenting and increased readability. Changed a log message to make it more clear where some warnings come from.