Fixed fatal error in update-loop (BLE_STATE_READ-state): retry_cnt is now initialized after succesfull reading.
Also added default-state in switch-case, where to go in, when unsupported state detected.

Added sensor-specific status indicator, indicating if accessed sensor is already enabled or not.

Added characteristic-reading (discoverCharacteristics and supporting function in gatt_att.c). There was problem,
that in newer SW-version of TI-sensor-tag, UUID/char-handle mapping was different compared  to older SW-version in other tag.
So it was bad idea for using hard-coded UUID-char-handle mapping. Now UUID is still hardcoded,
but handle is read by new function, so mapping is done dynamically every time, when connection to sensortag is established.

ble_demo gives gives now pitch/roll-angles (instead of temperature) to sensact-server (and IxGUI).
update-loop() requests pitch/roll from the accelerometer. There is also low-level support for magnetometer/gyroscope-data,
but those are not supported to upper level components.