Refactored dependencynode.py file.

Splitted long methods into smaller ones with smaller context to enhance
readability, maintenance, and to ease futur features integration.
Implemented complex business rules expansion

Business rules can now accept expansion expression on both host and service
items parts, allowing to write complex expnasion expression.

Expansion is now implemented using a filter based search allowing to
easily extend expansion criteria types.
Fixed a bug in business rule output processing.
Added tags expansion to hosts and fixed some typos
Renamed business_rule_tags to business_rule_labels
Merge pull request #996 from geektophe/bp_rule_service_tag

Added complex business rules expansion