Removed DHTMLXTREE code residue

Grepped the code for all DHTMLXTREE related occurrences. For e.g. -
1. node['id']
2. node['text']
3. node['im0'], node['im1'], node['im2']
4. node['item']
and deleted/addressed it.

#118
Merge pull request #1102 from AparnaKarve/gh118_remove_dhtmlxtree_code_references

Removed DHTMLXTREE code residue