Flight/ADC - Upper driver, check existence of lower driver functions.

Lower driver functions are checked for not NULL before calling them.
Rewriten PIOS_ADC_GetChannel function in a more readable manner.
Flight/ADC-Upper driver, store device pointer instead of opaque handler
Flight/ADC PCF8591 driver - Declare private functions as static
Flight/ADC PCF8591 driver - use stack variable for i2c buffer
Flight/ADC PCF8591 driver Fix identation and delete struc member init to null
Flight/ADC-PCF8591driver-Moved defines

From .h to .c the ones not needed outside of the driver code.
From .h to priv.h the ones needed outside of the driver code.
Deleted .h file not needed anymore.
Flight/ADC-Board init, ASSERT lower ADC driver return code

Do this before passing to upper ADC driver.
Flight/ADC-PCF8591 driver, define default adress on the driver priv.h file
Flight/ADC-ASSERT lower driver handler not found

Handlers are added to the upper driver lookup table in the init order,
so there shouldnt be any gaps. This ASSERT will check that.
Shared -taskinfo.xml fixed identation
Share-adcrouting.xml unwrap elementnames and options tags