Support several respiration modes (changeable at runtime)

Steps

[x] drop support of HW1 and HW2 (#53)
[x] drop support of different valves, pneumatic systems, flow-meters
[x] remove qualification and EOL modes (they are now available at runtime)
[ ] update STM32duino (#52)
[x] review and refactor internal variables of the pressure controller
[x] refactor pressure controller (it needs to be simpler)
[x] add support for several respiration modes, with only 1 implementation (the current)
[ ] add a dummy respiration mode to help development (only available when compiling in DEBUG mode)
[ ] allow to switch respiration modes at runtime using serial control