Library browser 1 update

Gives LB1 the ability to do some actions by ajax instead of redrawing the whole page.

Adds more-like-this feature to the database and to LB1.  We still need OPL problems to be tagged accordingly to see it in action (but it seems to work in test cases).

Adds more options to xmlrpc calls, e.g., when rendering a problem.  (When rerandomizing a problem in LB1, we want it to be styled exactly as it did originally.)

Invisible to the user, but starts to integrate reading/writing of library tags from a file (previously, only OPL-update could read tags).

Added another commit which cleans up a problem with rerandomizing problems, and improves OPL-update to handle blank dbsection/dbchapter tags in a better way.