[pr-comments] Decrease font size

[pr-comments] Remove docker connector section

This closes #1499.

This is not to fulfill what FLINK-3009 is originally asking,
but I'm piggybacking to contribute a docker environment with jekyll
so that users won't have to deal with environment versions.

Author: Jun Aoki <jaoki@apache.org>
Author: jaoki <jaoki@apache.org>

Closes #1363 from jaoki/dockerized-docgen and squashes the following commits:

7bf3661 [Jun Aoki] Added apache label
36869e7 [jaoki] [FLINK-3009] Add dockerized jekyll environment

- Changed layout (simple as possible)
- Fix broken version references in docs
- Update README
- Removed dead resources
- Reorganized content

[docs] Address PR comments

[docs] Address @ktzoumas comments

[docs] Fix download link

[docs] Fix front page stack link to Tez

This closes #606.

[FLINK-1697] [ml] Adds web documentation for alternating least squares. Adds web documentation for polynomial base feature mapper.

[ml] Adds comments

[ml] Set degree of parallelism of test suites to 2

[ml] Replaces FlatSpec tests with JUnit integration test cases in order to suppress the sysout output.

[ml] Adds missing clients-test jar

[docs] Sets jekyll's baseurl to http://ci.apache.org/projects/flink/flink-docs-master

[ml] Replaces JBlas by java netlib to avoid license issues of included fortran libraries

[ml] Adds com.github.fommil.netlib:core to license file

[ml] Adds Scala docs to FlinkTools

[ml] Adds comments to LabeledVector and the math package object

This closes #479.

Also dumped the stable release version in the docs config

Made exceptions for license check plugin more fine-granular.

This closes #250

  - corrected links to download page
  - corrected download urls
  - corrected wget shortcut for yarn setup
  - corrected links to faq in yarn setup
  - corrected guide for manual yarn build
  - FAQ layout

This can now be built standalone and then copied into the correct docs
folder of the website SVN.

The index page now has a short overview and a table of contents.

The switch to kramdown is necessary because I want to add tabs in the
documentation for code examples and Redcarpet does not allow markup
inside divs.

Before, some doc pages had "#" headings as toplevel headings while
others had "##" (which is the same as --- underlined headings). Now we
user level 2 everywhere. The page title is still a h1 heading.

- update _config.yaml of integrated documentation
- quick check on the quickstarts / build instructions to match the latest release
- quickstart.sh scrips now point to the correct versions.

[ci skip]

This closes #100

[ci skip]