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

pkg/zabbix/response_models.go

@@ -0,0 +1,35 @@
+package zabbix
+
+type Items []Item
+type Item struct {
+	ID        string     `json:"itemid,omitempty"`
+	Key       string     `json:"key_,omitempty"`
+	Name      string     `json:"name,omitempty"`
+	ValueType int        `json:"value_type,omitempty,string"`
+	HostID    string     `json:"hostid,omitempty"`
+	Hosts     []ItemHost `json:"hosts,omitempty"`
+	Status    string     `json:"status,omitempty"`
+	State     string     `json:"state,omitempty"`
+}
+type ItemHost struct {
+	ID   string `json:"hostid,omitempty"`
+	Name string `json:"name,omitempty"`
+}
+
+type Trend []TrendPoint
+type TrendPoint struct {
+	ItemID   string `json:"itemid,omitempty"`
+	Clock    int64  `json:"clock,omitempty,string"`
+	Num      string `json:"num,omitempty"`
+	ValueMin string `json:"value_min,omitempty"`
+	ValueAvg string `json:"value_avg,omitempty"`
+	ValueMax string `json:"value_max,omitempty"`
+}
+
+type History []HistoryPoint
+type HistoryPoint struct {
+	ItemID string  `json:"itemid,omitempty"`
+	Clock  int64   `json:"clock,omitempty,string"`
+	Value  float64 `json:"value,omitempty,string"`
+	NS     int64   `json:"ns,omitempty,string"`
+}