#22 add option to generate one-page report

[tmarenko]

Summary: https://github.com/lordmauve/flake8-html/issues/22

Approach:

• added --self-contained-html option as a marker to understand whether need to write one or multiple HTML files

• back.svg and file.svg files passes as Data URLs to one-page report

• report and source HTML files will be in the same one-page report. Navigation is done in self-contained.js by hiding elements with page classes.

• redesigned Jinja's templates:

1. base.html is a base for every template (index, reports, sources)
2. index.html now has additional logic based on self_contained marker
3. file-report.html and annotated-source.html are used for usual reports without --self-contained-html option
4. file-report-content.html and annotated-source-content.html are used both for usual and one-page report. Usual report uses them as template to fill, one-page report uses them to fill index.html template
5. bind-handler.js contains JS script from file-report.html in order to reuse it in different template