3232: Reorganized user guide

Major changes:

 * Now separate sections for how to use Arvados and how to develop for Arvados
 * Running a pipeline in workbench tutorial is simpler, involves fewer steps
 * New example pipelines which are biologically relevant
 * Working with data is its own section, and directs user to instructions on
   installing Python SDK in order to upload data remotely
 * Includes docker_image runtime constraint in examples
 * Introduces "run-command" wrapper before writing a script with the Python SDK
 * Added font awesome CSS and glyphs so documentation can use the same icons as Workbench.
Described with how to use "arv edit" in "Writing a pipeline".  Switched order of paragraphs in "introduction to crunch".  Grammar and wording tweaks.
Fixed one character typo "ghttp" -> "http" caught by linkchecker.
Updates in response to Radhika's comments.
Changed button label to "Add to project..." to match button introduced in #3452.
Merge branch 'master' into 3232-user-guide-updates
Fixed "Tutorial align using bwa mem and SortSam" template.  Tweaked
instructions for creating and editing template.  Fixed docker image in template
provided on "writing a crunch script".
Added explicit instructions on sample data to use for tutorial pipeline.
Merge branch '3232-user-guide-updates' closes #3232