version 0.1.1 Sprint 1 stm32 server

Added 4 different timers (each one with different frequency (period)).
Changes in app states (APP_ON, APP_SEND (BUSY), APP_OFF). When the stm32
receives 'S' the 100 ms signal is sent. With this version there is not a
periodic pwm signal sent to the beacons. At each demand the stm32
responds with one character via the serial protocol.