Fix VTOL enum shadowing

[julianoes]

This changes the enums used for various VTOL states to enum classes which makes them type-safe and should avoid shadowing.

This change was motivated by a Clang warning about shadowing of the enum const TRANSITION_TO_FW which was declared twice, once in vtol_type.h and once in standard.h.

In file included from /home/julianoes/src/Firmware/src/modules/vtol_att_control/vtol_att_control_main.cpp:49:
In file included from /home/julianoes/src/Firmware/src/modules/vtol_att_control/vtol_att_control_main.h:83:
/home/julianoes/src/Firmware/src/modules/vtol_att_control/standard.h:91:3: fatal error: declaration shadows a variable in the global namespace [-Wshadow]
                TRANSITION_TO_FW,
                ^
/home/julianoes/src/Firmware/src/modules/vtol_att_control/vtol_type.h:78:2: note: previous declaration is here
        TRANSITION_TO_FW = 1,
        ^
1 error generated.

This change only removes the shadowing but presumably these enums could be cleaned up and consolidated further.

FYI @sfuhrer