Add support for running code at start of publication process
Add support for running code at start of publication process

 - Add lbry.getFileInfoWhenListed()
 - Modify publish() to take an optional callback for when the file is
   listed.

lbryio/lbry-app,MaxiBoether/lbry-app,lbryio/lbry-app,jsigwart/lbry-app,MaxiBoether/lbry-app,lbryio/lbry-electron,MaxiBoether/lbry-app,lbryio/lbry-electron,jsigwart/lbry-app,akinwale/lbry-app,jsigwart/lbry-app,akinwale/lbry-app,lbryio/lbry-electron,akinwale/lbry-app,MaxiBoether/lbry-app,akinwale/lbry-app,jsigwart/lbry-app