HTML Report : Reorganize hierarchy and add an option to only generate the dynamic part instead of the full bundle

@pmouawad ([Bug 61458](https://bz.apache.org/bugzilla//show_bug.cgi?id=61458&redirect=false)):
See:

- https://stackoverflow.com/questions/45800316/jmeter-3-1-generate-dashboard-report-without-sbadmin2-folder

It would be interesting to allow the following:

- Have 1 resource folder to dependencies
- Have a "generated" folder containing 2 folders "html" (for the 3 html pages) and "js" (for graph.js)

This would allow the following:

- Distribute only the generated folder as the whole folder is big
- Possibly be able to generate only the "generated" files instead of generating the whole big thing
- Rely on 1 common resource folder

OS: All

Start by tracing the HTML report generation entry point and the current SBAdmin2/resource bundle, then compare how the three HTML pages and graph.js are emitted. Done means the proposed resource and generated/html and generated/js layout is produced, with an option to generate only the generated files while preserving full-bundle generation.

Written by the indexing model from the issue text.