[mms_codec] Ignore unknown headers and continue parsing

There's no reason to stop parsing. The assumption was that unknown headers
will follow the old ones that we do support but that turned out not to be
the case in the real life.
[mms-dump] Decode Previously-Sent-By/Date-Value
Merge pull request #32 from monich/unknown-headers

Ignore unknown headers and continue parsing
Version 1.0.13
[mms-dump] Cleaned up Response-status-value strings
[mms-lib] Limit receive task timeout by 10 minutes
Merge pull request #33 from monich/retrieve-timeout

Limit receive task timeout by 10 minutes
Version 1.0.14
[mms-engine] Made User-Agent configurable from the command line

I suspect that some issues in the field might be related to the value
of the User-Agent header. Better have it configurable.
Merge pull request #34 from monich/user-agent

Made User-Agent configurable from the command line
[mms_codec] Handle empty header values
[mms-lib] More tests
[mms-lib] Consistent output prefix for all tests
Merge pull request #35 from monich/empty-string

Handle empty header values
Version 1.0.15
[mms-ofono] Removed unnecessary include
[mms-ofono] Housekeeping
[mms-ofono] Fixed logging includes
[mms-lib] Removed MMS_CONNECTION_ERROR

It's not being used.
[mms-lib] Handle X-Mms-Read-Report in M-Retrieve.conf

This tells us whether the sender requested a read report.