Backend: implement alerting query (#847)

* Unit tests for backend

* minor change

* Implemented querNumericItems in backend

* Added query type

* Set alerting to true

* Return TimeSeries from History

* Updated alerting feature

* Fix params marshal error

* Fix params more

* Update zabbixAPIConnector.js

* Numbers, I guess

* Params Output Type

* Output marshaling

* Unmarshal and decoder error catch

* HistoryPoint and Unmarshal fixes

* Unmarshal to History

* Revert "Update zabbixAPIConnector.js"

This reverts commit e0ffdff859b6f920893a47a709493f8076e38ef4.

* Fix unmarshaling for real

* Time range integer

* Use more zabbix.Items

* Update response_models.go

* Update zabbix_api.go

* Update models.go

* Update zabbix_api.go

* Tests

* Adding more unit tests and cleaning up additional logging

* Make history request param a pointer

* Actually store datasource in cache

* Debug logs and timings

* Handle panics gracefully

* Updated Regex filter parsing

* Removed must compile

* Clean up regex filter

go.mod

@@ -13,6 +13,7 @@ require (
 	github.com/kr/pretty v0.1.0 // indirect
 	github.com/patrickmn/go-cache v2.1.0+incompatible
 	github.com/pkg/errors v0.8.1 // indirect
+	github.com/stretchr/testify v1.3.0
 	golang.org/x/net v0.0.0-20190724013045-ca1201d0de80
 	golang.org/x/sys v0.0.0-20191010194322-b09406accb47 // indirect
 	golang.org/x/text v0.3.2 // indirect