#343 Implement private tags

[Ahasuerus]

Currently some tags are user-specific, e.g. "to read 1977". We need to add a new field to the tag mapping table to mark them "private". A private tag will not be displayed on the Title and Summary pages unless the currently signed in user is the owner of the tag. We also need to create a moderator-only page to delete inappropriate tags and/or make them private.

[Ahasuerus]

Implemented in:

biblio/authortags.py 1.3
biblio/biblio.py 1.31
biblio/se.py 1.25
biblio/tag.py 1.9
biblio/title.py 1.62
biblio/usertag.py 1.3
common/SQLparsing.py 1.97
common/isfdb.py 1.48
mod/change_tag_status.py 1.1
mod/TARGETS 1.29
scripts/add_private_tag.sql 1.1

Installed in r2014-49 on 2014-01-21. Closing.