feat(influxdb): add default interval setting

closes #1552

public/app/plugins/datasource/influxdb/datasource.ts

@@ -19,7 +19,7 @@ export function InfluxDatasource(instanceSettings, $q, backendSrv, templateSrv)
   this.name = instanceSettings.name;
   this.database = instanceSettings.database;
   this.basicAuth = instanceSettings.basicAuth;
-
+  this.interval = (instanceSettings.jsonData || {}).timeInterval;
   this.supportAnnotations = true;
   this.supportMetrics = true;
 

public/app/plugins/datasource/influxdb/partials/config.html

@@ -33,3 +33,20 @@
 </div>
 
 
+<br>
+<h4>Default query settings</h4>
+<div class="tight-form last">
+	<ul class="tight-form-list">
+		<li class="tight-form-item" style="width: 200px">
+			Group by time interval
+		</li>
+		<li>
+			<input type="text" class="input-medium tight-form-input input-xlarge" ng-model="ctrl.current.jsonData.timeInterval"
+			spellcheck='false' placeholder="example: >10s">
+		</li>
+		<li class="tight-form-item">
+			<i class="fa fa-question-circle" bs-tooltip="'Set a low limit by having a greater sign: example: >10s'" data-placement="right"></i>
+		</li>
+	</ul>
+	<div class="clearfix"></div>
+</div>