Creating a plugin for TeamCity

Need to develop a plugin for TeamCity. Plugin must run code before each build. Should be able to configure the settings for the plugin in "Build step" menu. I did not find more information how to make a web interface and get out of there settings for the plugin. I found a few examples. Here is one of them:

• https://github.com/Blazemeter/blazemeter-teamcity-plugin/blob/master/server/src/META-INF/build-server-plugin-BlazeMeter.xml - Spring xml with beans implamentetion.
• https://github.com/Blazemeter/blazemeter-teamcity-plugin/blob/master/server/src/com/blaze/runner/BlazeMeterReportTab.java - class, which in theory is responsible for the web interface.

We can see that the class has a constructor:

public BlazeMeterReportTab (final PagePlaces pagePlaces, final SBuildServer server) {
      super (TAB_TITLE, TAB_CODE, pagePlaces, server); 
      this.server = server; 
}

However, in bean it has not been initialized:

<bean id="blazeReportTab" class="com.blaze.runner.BlazeMeterReportTab"
  init-method="register">
    <property name="placeId" value="BUILD_RESULTS_TAB" />
    <property name="pluginName" value="BlazeMeter" />
    <property name="includeUrl" value="reportPage.jsp" />
</bean>

Can somebody help me understand this point? Maybe there is a detailed guide how to develop a plugin for TeamCity with examples?