usb: Don't override control transfer direction

start_control_return() shouldn't set ep0_data_stage_direc to IN because
start_control_return() can also be used for OUT control transfers with no
data stage.  Setting ep0_data_stage_direc to IN, in this case, caused the
callback to not get called when the transaction was complete.
bootloader: Perform the reset in the transfer callback

Now that the callback has been fixed for transfers with no data stage,
handle the bootloader's reset command in the callback. This way the
transfer completes before the reset occurs, causing the host to see a
successful transfer (and not report an error because the device was reset
before the transfer was complete).
bootloader sw: Don't squash the return value for send_reset()
project: Add MPLABX-created empty attributes

MPLABX 1.8 wants to add these, so here they are.
all: Touch up the README and change the branding to M-Stack

Change "Signal 11 USB Device Stack" and "Signal 11 USB Stack" to M-Stack.
bootloader, bootloader sw, host_test: Ensure proper license headers

Ensure that all source files have a proper license header stating their
license.