Add support for workflow

Acceptance criteria from the plugin maintainer (oleg_nenashev) 

• UsedCustomToolsAction RunAction2, which tracks the list of required tools
• "Install custom tool" simple build step, which adds the tool to the scope of the task (AbstractProject or Pipeline's node() scope). Stores data in UsedCustomToolsAction. Pipeline alias - e.g. customTool()
• Ability to contribute environment variables for launched scripts, likely with a new LauncherDecorator method (decorate(Launcher launcher, Job job, Node node) or so) - depends on JENKINS-TODO, can be done in a compatible way
• Update the DecoratedLauncher implementation and to move it outside the BuildWrapper to the new LauncherDecorator
• New DecoratedLauncher implementation pulls information about tools from UsedCustomToolsAction and then initializes it, similarly to what it does now with pulling from the Build Wrapper
• Automatic test(s) for the common use-cases in Pipeline (see the requirements below)
• Documentation, can be written in a new page within the GitHub repository (Wiki must die soon). This documentation should describe the logic and provide examples.

Extra requirements:

• The version engine is supported including the Tool Version parameter. Should be no problems with that, but needs testing
• The resolution of variables in the step takes other Node and Job environment variables into account

Nice2have, optional:

• Some UI, which improves tracking of tool usage in UsedCustomToolsAction - really important for multi-log Pipeline
• Support definition of tools on the global level (for all node() calls)
• CustomToolsBuildWrapper is reworked to the SimpleBuildWrapper
  • oleg_nenashev: Not really required if there is a buildStep described above
• Common tool() step is able to invoke the customTool() logic somehow.
  • oleg_nenashev: Not sure if it is doable without new core APIs