Introduce a new configuration variable for KWIC which specifies wether html is
rendered or shown as plain text. The property is defined as follows:
"escape_html:<true|false>".
Escape a html tag in grid visualization. This is the default behaviour up to the
future.
Make also the grid visualization html tags treatment configurable.
Make also the gridtree visualization configurable for escaping html tags.
Escape html tags in corpora node annotation values, so that they are shown in
annis-visualization. This is the default behaviour from now on for:

- KWIC
- grid visualization
- grid tree visualization

If html tags should not be rendered as text, it is possible to change this in
the resolver_vis_tab table. Simply add "escape_html: false" in the mappings
column.

closes #227

Merge branch '227' into develop