fix: change cloudant.since logic to prefer saved offset, if present

[tomblench]

fixes #124

[ricellis]

The change seems fine, but I wonder if we should do three additional things here, namely:

1. Update

   cloudant-kafka-connector/src/main/resources/message_en_US.properties

   Line 46 in 9c52db6

   CloudantLastSeqNumDoc = Last update sequence identifier to resume from. \

   to indicate what the behaviour is when unset (since it will no longer show a default value of "0" I think).
2. Regenerate the config doc since the default is now different (and to include above update).
3. Add a test so we don't accidentally regress this at some point.

[tomblench]

The change seems fine, but I wonder if we should do three additional things here, namely:

1. Update

   cloudant-kafka-connector/src/main/resources/message_en_US.properties

   Line 46 in 9c52db6

   CloudantLastSeqNumDoc = Last update sequence identifier to resume from. \

   
   to indicate what the behaviour is when unset (since it will no longer show a default value of "0" I think).
2. Regenerate the config doc since the default is now different (and to include above update).
3. Add a test so we don't accidentally regress this at some point.

1. could you please look at 64386b4 - i'm not totally sure what the message should look like here so i'm open to suggestions (eg should it be more explicit that this behaviour is used to track the latest sequence between restarts)
2. sure
3. just a unit test for the defaults? that should be pretty easy

[ricellis]

+1, small nit

[ricellis]

+1 a couple of nits on copy/paste test comments

[tomblench]

thanks @ricellis for spotting those copy/pastes