Changes

Some improvements to sortable tables.
* src/main/web 393a017...3e43f3a (1):
 > Port sort icons adjustment to the sortable.js solution
* src/main/xproc 25d2c7e...4328b72 (4):
 > Incipit: Removed duplicate nodes from the incipit node set
 > Detection for empty (instead of missing) pages.
 > Refactored metadata2json to use collection() approach.
 > Refactored document metadata to jsonutils.xsl
 (commit: c10c051)