update jinja template to have getCell function

Author: Jaquier Aurélien Tristan

bluepyopt/ephys/templates/cell_template.jinja2

@@ -42,6 +42,10 @@ begintemplate {{template_name}}
   public all, somatic, apical, axonal, basal, myelinated, APC
   objref all, somatic, apical, axonal, basal, myelinated, APC
 
+obfunc getCell(){
+        return this
+}
+
 proc init(/* args: morphology_dir, morphology_name */) {
   all = new SectionList()
   apical = new SectionList()