Line in jack detect

Since rev7 you can tell if something is connected in line in with the SR node

Which goes to the port expander

Give this a C and python api.

added feature label

mentioned in issue #17

mentioned in issue #19 (closed)

assigned to @schneider

mentioned in commit 60f2d4e1

mentioned in merge request !90 (merged)

mentioned in commit 864b26f3

mentioned in commit f8c0cb9b

closed with merge request !90 (merged)

closed with commit f8c0cb9b

mentioned in issue #131 (closed)