docs/app: add docs for deployment hooks

Related to #347.
docs/apps/client: remove hooks docs from wrong place

WTF trophy.

Related to #347.
docs/overview: fix reference to hooks page, and update terms

Related to #347.
quickstart/ruby: update hooks information

Related to #347.
docs/css: bigger font
docs/quickstart/ruby: improve wording
docs/quickstart/python: update informations about hooks

Related to #347.