Handle deletions differently than additions/modifications

[thisisaaronland]

Currently we achieve this by not receiving any deletions (pending a finalized version of the filtered branch of webhookd) but there are probably reasons we want to be notified and do something.

This is blocked on whosonfirst/go-webhookd#12

[thisisaaronland]

For example, sometimes we end up with PRs that have a bunch of commits for files that were added and then removed (before being pushed to master) and end up with stuff like this:

updated APP [12:39] 
19:39:10.593511 [wof-updated][:popcorn: [whosofirst-data-4]] STATUS Time to process (pull) whosonfirst-data: 7m35.894139799s


[12:39] 
19:39:11.663949 [wof-updated][:popcorn: [whosofirst-data-4]] ERROR failed to index Elasticsearch exit status 1 (/usr/local/bin/wof-es-index-filelist --host internal-whosonfirst-elasticsearch-1139831451.us-east-1.elb.amazonaws.com --port 9200 --index spelunker /tmp/updated911272537)


[12:39] 
19:39:11.748020 [wof-updated][:popcorn: [whosofirst-data-4]] STATUS Time to process (elasticsearch) whosonfirst-data: 1.06270209s


[12:39] 
19:39:17.324086 [wof-updated][:popcorn: [whosofirst-data-4]] FATAL Failed to index /tmp/updated037045747 mode because open /usr/local/data/whosonfirst-data/data/110/897/911/1/1108979111.geojson: no such file or directory

See also: whosonfirst-data/whosonfirst-data#824 (comment)