FlyingF4: switch to internal flash

There aren't many people using this and it allows them to use
the internal flash and a simpler shield.  We can add support
for external flash for other things again if the need arises.
PIOS_INCLUDE_SETTINGS: delete unused flag
FlyingF4: restore panic LEDs for flash failure
DiscoveryF4: add panic LEDs for flash failure
FlyingF4: enable storing waypoints in external flash

A flag PIOS_INCLUDE_EXTERNAL_FLASH_WAYPOINTS enables storing the waypoints
in an external flash chip, which allows for many more than internal storage.
This also preserves the code for using the external flash chip.

Alternatively waypoints could be stored internally on the F4 but since there
are very few FlyingF4 users this is somewhat arbitrary.
FlyingF4: use macro for FLASH_SECTOR_64KB
Merge pull request #705 from peabody124/flyingf4_int_flash

FlyingF4: switch to internal flash