Fix nebulous Twig error caused by indexing a variable w/ a Twig_Markup...

Fix nebulous Twig error caused by indexing a variable w/ a Twig_Markup instance. Should not use {% set %}...{% endset %} if value will be used as index.

plugins/CoreHome/templates/datatable_cell.twig

-{% set tooltipIndex %}{{ column }}_tooltip{% endset %}
+{% set tooltipIndex = column ~ '_tooltip' %}
 {% if row.metadata[tooltipIndex] is defined %}<span class="cell-tooltip" data-tooltip="{{ row.metadata[tooltipIndex] }}">{% endif %}
 {% if not row.idsubdatatable and column=='label' and row.metadata.url is not empty %}
     <a target="_blank" href='{% if row.metadata.url|slice(0,4) not in ['http','ftp:'] %}http://{% endif %}{{ row.metadata.url }}'>
@@ -20,4 +20,4 @@
 {% if not row.idsubdatatable and column=='label' and row.metadata.url is not empty %}
     </a>
 {% endif %}
-{% if row.metadata[tooltipIndex] is defined %}</span>{% endif %}
+{% if row.metadata[tooltipIndex] is defined %}</span>{% endif %}
\ No newline at end of file