metadata stored in wbrequest.user_metadata and available to all templates
collections manager: refactor to use subparsers, add list collections and set metadata commands
update tests for new commands
index template: use user metadata title for collections listing
search template: display all metadata and title, if available
option to index and merge instead of reindexing whole dir, #74
additional testing for recursive indexing, index merge
timeutils: add timestamp20_now() function