MOD: Split scanevents into IptcParser and Scanner classes

Necessary step for issue #4
ADD: checkboxes for selecting thumbnails

Necessary step for issue #4
ADD: addTags form
ADD: remember selected thumbnails between form posts

Necessary step for issue #4
FIX: allow addition of non-existant tags
ADD: add iptc to photo

Necessary step for issue #4
ADD: deletion of tags

Necessary step for issue #4
FIX: update changed photo instead of delete+add

Last step to close #4
Merge branch 'issue004'

Support addition and deletion of tags directly from the web interface.