Add Gemfile to make local development easier

As described in https://help.github.com/articles/using-jekyll-with-pages
move lead graf below title
make Kosovo/UK comparison more readable/useful
use "Request state" wording

Had been "States of request" to avoid "Request" to sound like a verb,,,
but it's weird because everywhere these are simply called "request
states" and the title being different was confusing me.
update doc summary
Fix typo in param name

This connection param is consulted in config/initializers/alaveteli.rb to see whether to load our patch for constraint disabling from lib/no_constraint_disabling.rb
Merge branch 'gh-pages-gemfile' into gh-pages
Merge branch 'gh-pages' of ssh://git.mysociety.org/data/git/public/alaveteli into gh-pages
Merge branch 'gh-pages-fix-typo' into gh-pages
Plugin install method now obsolete.

Superceded by rake task.
Fix path
Whitespace changes.
First draft of new theme editing section
track what's been included/missed from docs/ dir
fix bad links to .md docs: should be code.alaveteli pages
delete redundant anchor tag (Jekyll autogenerates it)
markdown: remove space to preserve double hyphen
add postfix MTA setup instructions/example

from doc/INSTALL-postfix.md
rename installing/exim4 to installing/email

because it's no longer just about exim but also postfix.
This commit includes updating links in the docs to the new page.
Fix some syntax/naming issues.