Test bitarray assignment to global register.

Big-endian bitarrays and normal integers should result in the same
output/behavior. E.g. field=253 should result in the same output as
field=bitarray("11111101").
Delay first injection if it starts SEQ.

This way, there is time for the signal to be high before it goes low to
inject.
Add extra control configuration before output.

Configuration sets HITLD and S0 to 0 again (as specified in the FE-I4
manual).
Clean up scan_inject.py.

Remove a print statement, change repeated commands to a for loop.
Fix bug: SEQ writes the wrong length of injection.

Bug was introduced in commit 9655a87354d089de716bc417cada90c02fb078b1.

Fixed by keeping track of "number of bits written to sequence" and
updating that value in the specific case that the first command is an
injection (dealt with in a special way).

Along the way, changed the _block_length member variables to a dict,
_block_lengths[...]. Acceptable keys are currently 'pixel', 'global',
and 'inject'.
Change test_multi_column.py into a unittest.
Set up to debug injection output.
Fix order of LD_IN0_7.

Should be backwards.
Allow command-line argument to change column #.

Also commented out the pixel sr output.
Update LD_IN0_7 bitarray to be reversed (normal).

Responding to the change from commit 98b6add2.
Merge branch 'feature/injection' of github.com:musicalrunner/atlas_usbpix_control into feature/injection