Simplification in A3D structure, removed outdated functionalities

Removed all optionnal exe args except restart, now snowpack and eb are always constructed, nocompute option has been removed, and drift has to be enabled using ENABLE = TRUE in the SNOWDRIFT section. The runoff module has been de-activated, and the data assimilation module commented out. The flow of AlpineControl::Run has been simplified, now it is clear which module does what and update which grids.