changed implementation of tx-gain setting/handling  (now set upon enabling the TX board), because new TXB (v5 and newer) disables poti when inactive (off)

changed interface of txgain (appended Level, added function to obtain number of tx gain levels, added number of gain levels to ACI response

fixed a bug that accidentally included (empty) sim bootloader instead of platform bootloader; stripped down makefile and removed stm-legacy makefile alltogether; yet need to shift stuff from platform makefiles to generic one