Add extra MSP commands to allow settings to be made via a GUI in
addition to setting via the CLI.

Note: MSP_CONFIG from baseflight
bc68d89983d762d35cc1cf5e3fa0c2cf03287b70 will not be supported because
more specific commands exist in cleanflight.

MSP_MISC and MSP_CONFIG are good examples of single responsibility
violations.
Disable MPU6500 on EUSTM32F103RC because the driver autodection is not
implemented yet. See #119.