Add all modes to label

[nbrachet]

Switched the UAS into AUTO mode and the app showed the mode as GUIDED.
Here are all the modes:
ARDUCOPTER_MODE_STABILIZE=0, // hold level position
ARDUCOPTER_MODE_ACRO=1, // rate control
ARDUCOPTER_MODE_ALT_HOLD=2, // AUTO control
ARDUCOPTER_MODE_AUTO=3, // AUTO control
ARDUCOPTER_MODE_GUIDED=4, // AUTO control
ARDUCOPTER_MODE_LOITER=5, // Hold a single location
ARDUCOPTER_MODE_RTL=6, // AUTO control
ARDUCOPTER_MODE_CIRCLE=7, // AUTO control
ARDUCOPTER_MODE_LAND=9, // AUTO control
ARDUCOPTER_MODE_OF_LOITER=10, // Hold a single location using optical flow sensor
ARDUCOPTER_MODE_DRIFT=11, // DRIFT mode (Note: 12 is no longer used)
ARDUCOPTER_MODE_SPORT=13, // earth frame rate control
ARDUCOPTER_MODE_FLIP=14, // flip the vehicle on the roll axis
ARDUCOPTER_MODE_AUTOTUNE=15, // autotune the vehicle's roll and pitch gains
ARDUCOPTER_MODE_POSHOLD=16 // position hold with manual override
If a mode is received that is not in this list the label should show the numeric value of the mode (rather than some other mode)

Note: there should be no change to the mode displayed in the menu.

[nbrachet]

0.2.5.8 shows all those modes in the menu.
The intended behavior is to have the ability to correctly display the mode in the label (in case the mode is changed by the transmitter for example), but only offer the few modes in the menu,