Hide token annotations in KWIC is configurable via mappings in resolver_vis_tab.
The key is "hidden_annos" followed by a comma separated list of qualified
annotation names.

closes #256
Avoid nullpointer errors when no session is available.
Add document path to document browser table and use this as row index, since the
document must be unique by annis database schema definition.

closes #261
Merge branch 'doc_browser/corpus_column' into release/3.1.0-alpha