Enable template options

# What it does
Enables template options via --opt VAR=SOMETHING

# What it does NOT
Break how everything used to work, so old templates still work

# Description
```
$ okconfig addtemplate www.okconfig.org --template http \
        --opt VIRTUAL_HOST=vhost.okconfig.org \
        --opt SEARCH_STRING=something
Saved /etc/nagios/okconfig/hosts/default/www.okconfig.org-http-vhost.okconfig.org.cfg
```

Contents of the file (/etc/nagios/okconfig/hosts/default/www.okconfig.org-http-vhost.okconfig.org.cfg) become
```
define service {
	use			okc-check_http
	host_name		www.okconfig.org
	contact_groups		default
	service_description	HTTP vhost.okconfig.org
	#check_command		okc-check_http

	__VIRTUAL_HOST		vhost.okconfig.org
	#__URI			/
	__SEARCH_STRING	something
	#__RESPONSE_WARNING	2.0
	#__RESPONSE_CRITICAL	10.0
	#__PORT			80
	#__ON_REDIRECT           follow

}
```

Then there is the configuration for the template options.
/usr/share/okconfig/examples/http.yml
```
filename:   "{HOSTNAME}-http-{VIRTUAL_HOST}.cfg"
parms:
    VIRTUAL_HOST: 
        default:    k:HOSTNAME
        summary:    Virtual host to query for
    URI:
        default:    /
    SEARCH_STRING:
        default:    
    RESPONSE_WARNING:
        default:    2.0
        summary:    Response time in seconds till warning
    RESPONSE_CRITICAL:
        default:    10.0
        summary:    Response time in seconds till critical
    PORT:
        default:    80
    ON_REDIRECT:
        default:    follow
        summary:    Action to on redirects, eg <ok|warning|critcal|follow|sticky|stickyport>

```

It still uses the example file which now looks like this:
```
define service {
	use			okc-check_http
	host_name		HOSTNAME
	contact_groups		GROUP
	service_description	HTTP ^VIRTUAL_HOST
	#check_command		okc-check_http

	__VIRTUAL_HOST		^VIRTUAL_HOST
	#__URI			^URI
	#__SEARCH_STRING	^SEARCH_STRING
	#__RESPONSE_WARNING	^RESPONSE_WARNING
	#__RESPONSE_CRITICAL	^RESPONSE_CRITICAL
	#__PORT			^PORT
	#__ON_REDIRECT           follow

}
```


@palli the feature makes sense for any template that can have multiple instances of template. http being a fine example, another one, which is actually the one that drove me to make this change, mssql template. It's semi common to run multiple instances where you want all or some of the checks per instance. There you run into quite a headache to copy and rename many service checks and okconfig doesn't do a great job.