RUN-2412: Plugin property mapping

[jsboak]

Two enhancements:

1. propertyResolver added so that properties set on the project/framework level are retrieved
2. a new property can be set on project/framework level to force plugin to use proxy-settings set on the JVM (see comment below)

[jsboak]

new property needs to be set on project (or framework):
project.plugin.WorkflowStep.edu.ohio.ais.rundeck.HttpWorkflowStepPlugin.useSystemProxySettings=true

This tells the plugin to use the JVM proxy settings as set here