records: allow developer_data_id messages without set application_id

[flokli]

It seems like the ELEMNT BOLT writes messages without application_id
set. Check this in add_dev_data_id(message) and store None in
DEV_TYPES[dev_data_index]['application_id'].

[pR0Ps]

Thanks, this looks like a pretty straightforward fix. Would you be able to also include a small example fit file that causes this issue (and a test that loads it as well)?

EDIT: This will fix #35
EDIT2: The example files provided in this issue exhibit the problem (ask permission if you intend to add them instead of your own files).

[flokli]

@pR0Ps I added a small example file and a test. Also, please have a look at #37, it contains some fixes for the testsuite (could also add travis integration in a follow-up, if you like)