bst_consyn_harvest: Various fixes

* Adds 2 new execution modes to exctract and convert
  files from a zip package or a list of packages

* Appends a message with the summary of the harvest
  on the end of the bibsched log

* Reports a summary of the harvest to the desired
  receipient (CFG_CONSYNHARVEST_EMAIL)

* Fixes imports

* Deletes the feed file from disk