GWT Super DevMode from the command line

[azatsarynnyy]

CQ https://dev.eclipse.org/ipzilla/show_bug.cgi?id=14390

What does this PR do?

Introduces a way of launching GWT's CodeServer (Super DevMode) for Che sources with a command line and not depend on GWT plugin provided by the concrete IDE: GWT Eclipse Plugin, GWT Plugin for IntelliJ IDEA Ultimate Edition etc.

How does it work?

In order to launch GWT Super DevMode for the Che sources the following command is proposed to use:
mvn clean gwt:codeserver -pl :assembly-ide-war -am -Psdm
There're three main parts:

• The main command, mvn gwt:codeserver, relies on the aggregator goal codeserver of the net.ltgt.gwt.maven:gwt-maven-plugin. This goal runs GWT's CodeServer with the necessary parameters and the correct classpath.
• It's recommended to use parameters -pl :assembly-ide-war -am in order the speed-up launching of the GWT's CodeServer by skipping the most of the maven modules which don't contain the client code.
• clean cycle and sdm maven profile are mandatory for now but they'll become unnecessary after complete migration to the new maven plugin. Since we still use both the legacy org.codehouse.mojo:gwt-maven-plugin and the new net.ltgt.gwt.maven:gwt-maven-plugin all settings related to the new plugin have been placed within the separate maven profile sdm in order to avoid some configuration troubles. It's planned to remove this profile after complete migration to the new maven plugin.

So now there're several options available for launching GWT Super DevMode with the proposed command line.

Launch GWT Super DevMode (inside a container) working on the Che sources in Che IDE

Caveat: GWT CodeServer works really slow inside a Docker container.

• Import Che project's sources into your workspace
• Create a command GWT SDM for Che within the Run goal
• Make sure that che project is selected in the Project Explorer
• Run the command created in the previous step
  

Launch GWT Super DevMode on the local machine (works with any IDE)

• Go to the Che project's sources root folder. In case of developing in Che IDE go to the host folder where :/data volume is mounted, then go to your workspace's folder within instance/data/workspaces/ and there you should find che folder contains your Che's project sources. E.g., cd /home/user/che/data/instance/data/workspaces/wksp-2hpp/che.
• Launch GWT CodeServer with a recommended command: mvn clean gwt:codeserver -pl :assembly-ide-war -am -Psdm

Launch GWT Super DevMode in IDEA (including IDEA CE w/o GWT plugin provided)

What issues does this PR fix or reference?

#2595

Release Notes

Docs PR

[codenvy-ci]

Build # 4002 - FAILED

Please check console output at https://ci.codenvycorp.com/job/che-pullrequests-build/4002/ to view the results.

[codenvy-ci]

Build success. https://ci.codenvycorp.com/job/che-pullrequests-build/4015/

[azatsarynnyy]

will be provided as part of #6602