Added Note for Eclipse users. Minor updates in Spark doc

docs/samples/analytics/spark-integration-with-thingsboard.md

@@ -17,10 +17,10 @@ However, most of the real-life use cases also require the support of advanced an
 This tutorial will demonstrate how you can:
 
  - route telemetry device data from ThingsBoard to Kafka topic using the built-in plugin.
- - aggregate data from multiple devices using simple Apache Spark application.
+ - aggregate data from multiple devices using a simple Apache Spark application.
  - push results of the analytics back to ThingsBoard for persistence and visualization.
 
-Of course, analytics in this tutorial is quite simple, our goal is to highlight the integration steps.
+The analytics in this tutorial is, of course, quite simple, but our goal is to highlight the integration steps.
 
 ### Overview
 
@@ -46,10 +46,10 @@ We also assume that you are familiar with Kafka and Spark and have also prepared
 
 ### ThingsBoard configuration steps
 
-### Step 1. Configuration of Kafka Plugin
+### Step 1. Kafka Plugin Configuration
 
 We need to configure Kafka Plugin that will be used to push telemetry data to Kafka. 
-You can find detail description of Kafka Plugin [here](/docs/reference/plugins/kafka/).
+You can find the detailed description of Kafka Plugin [here](/docs/reference/plugins/kafka/).
 
 [**Download**](/docs/samples/analytics/resources/kafka_plugin_for_spark_streaming_sample.json) the json with plugin descriptor 
 and use this [**instructions**](/docs/user-guide/ui/plugins/#plugin-import) to import it to your instance.

docs/samples/raspberry/resources/gpio.py

@@ -11,7 +11,7 @@
 
 
 # The callback for when the client receives a CONNACK response from the server.
-def on_connect(client, userdata, rc):
+def on_connect(client, userdata, rc, *extra_params):
     print('Connected with result code ' + str(rc))
     # Subscribing to receive RPC requests
     client.subscribe('v1/devices/me/rpc/request/+')

docs/user-guide/contribution/how-to-contribute.md

@@ -47,6 +47,8 @@ A build will generate all the *protobuf* files in the *application* module that
 Next, import the project into your favorite *IDE* as **Maven** project. 
 See separate instructions for [**IDEA**](https://www.jetbrains.com/help/idea/2016.3/importing-project-from-maven-model.html) and [**Eclipse**](http://javapapers.com/java/import-maven-project-into-eclipse/).   
 
+**NOTE:** If you are using Eclipse, after the maven project is imported to the IDE, We recommend you to disable Maven Project builder on **ui** project. This will improve the Eclipse performance *a lot*, because it will avoid Eclipse Maven builder from digging in node_modules directory (which is unnecessary and only causes Eclipse to hang). To do this, right-click on **ui** project, go to **Properties -> Builders**, and then uncheck the **Maven Project Builder** checkbox and then click **Ok**.
+
 #### Database
 
 By default, ThingsBoard uses embedded HSQLDB instance which is very convenient for evaluation or development purposes.