Making 'Related Rerources' title smaller in the sidebar

 - Add link to actual GSG
 - Add Tutorials section
 - Clean up Understanding section

Note, this was processed using the following command line:

    fpp --input=README.ftl.md --output=README.md

and output suffers from the bug detailed at:

    https://www.pivotaltracker.com/story/show/52221207

In *Create a main class* moved first paragraph of text to beginning of
section, before code.>>>>>>> upstream/master

- Change admonition style to use blockquote syntax

 - Revise all exposition
 - Remove gradle artifacts and instructions for now
 - Eliminate @Configuration class
 - Convert tabs to spaces in .java and .xml files
 - Preserve empty directory structure in 'initial'

[http://localhost]() syntax used previously doesn't actually work. Link
is created, but link is back to self.

Per a [hot tip][1], now using <http://localhost> syntax, which works
perfectly.

[1]: https://github.com/vmg/sundown/issues/132#issuecomment-8774103

 - http://foo.com will auto-link
 - http://foo.com:8080 will too
 - http://localhost won't
 - http://localhost:8080 won't either

Workaround is to wrap in link syntax, e.g.

 - [http://localhost:8080]()

Per http://github.github.com/github-flavored-markdown/

Introduce mocked-up macro syntax with the goal of eliminating
duplication of common sections, introductions, disclaimers, etc.

See gs-macros.md[1] for expanded values.

[1]: https://github.com/springframework-meta/springframework.org/tree/master/doc/gs-macros.md

 - Standardize capitalization across title and subsection headers
 - Standardize grammar of title and subsection headers
 - Standardize link format

Also now wrap Maven/Gradle sections in <span> tags with 'maven' and
'gradle' class values to allow us to apply CSS to these to hide or show
based on value of Maven / Gradle toggle control in UI. Ideally this
should be a <div>, but by default Markdown syntax is not supported (i.e.
parsed) within divs. See
http://daringfireball.net/projects/markdown/syntax#html for details.

 - See ./test/run.sh
 - See https://drone.io/github.com/springframework-meta/gs-rest-service

Fix gradle build dependencies

The 'start' version has missing bits in the pom.xml as well as differences in what
the guide said. After comparing with 'complete', made the fixes and updated the
guide appropriately so it should work top-to-bottom if you use 'start' and really
copy-n-paste your way along.

Add plugin repositories for snapshots

Work in progress, pushing now in order to share with rest of content
team.

Initial runnable app working with Maven and Gradle deps