Support of tags for host prototypes

Summary

Currently host prototypes do not support tags, however this functionality will be very useful for discovery of cloud resources when each discovered host may contain its own set of tags with useful information (datacenter, instance type, resource type, etc).

Acceptance

Zabbix must support tags for host prototypes:

1. Tags of host prototypes must support LLD macros in tag values
2. LLD discovery must be enhanced to take into account tags of host prototypes
   1. Tags of host prototype must not overwrite host tags
3. UI enhancements
   1. New tab 'Tags' must be added to host prototype form
   2. Import/export of host prototypes will be extended to include information about tags
4. API 
   1. Corresponding API methods must be updated to include information about tags of host prototypes

Use cases

1. I want to use information returned by LLD as tag value of a discovered hosts