docs(all): Cut fluff

This is an attempt at taking my own writing advice seriously.
I've gone through and tightened up the language of a bunch of the docs,
especially the first sentence of the doc which summarizes the purpose.
Merge pull request #6716 from ewinslow/docs-fluff

docs(all): Cut fluff
docs(moved): use :orphan: instead of lying toctree
docs(js): use proper title markup

The previous markup matched other heading levels within the
document itself, so sphinx was getting confused and putting
the sub-headings into the top-level table of contents.
Merge pull request #6719 from ewinslow/docs-orphans

docs(moved): use :orphan: instead of lying toctree
docs(guides): add web services dev guide
Merge pull request #6720 from ewinslow/docs-js

docs(js): use proper title markup
Merge pull request #6718 from ewinslow/docs-web-services

docs(web-services): add web services dev guide
docs(code): merge coding_standards into contribute/code.rst
docs(plugins): added instructions on upgrading plugins for Elgg 1.9
Merge pull request #6680 from juho-jaakkola/plugin_upgrade_docs

Instructions on upgrading plugins for Elgg 1.9
chore(session): moves persistent login logic to service

This adds a persistent login service, which centralizes this logic and
documents the processes and legacy information.

Fixes #6631
chore(upgrade): Replaced custom XHR upgrade views and js with a generic implementation
docs(code): add docs on testing and cleanup

Simplifies PHP guidelines, mentions complexity
Merge pull request #3 from mrclay/ewinslow-docs-code

docs(code): add docs on testing and cleanup
docs(code): fix whitespace warnings
Merge pull request #6633 from mrclay/persistent_login_svc

chore(session): moves persistent login logic to service
Merge pull request #6721 from ewinslow/docs-code

docs(code): merge coding_standards into contribute/code.rst
fix(git): Igorning revert commits in Travis and in commit-message git hook.
Merge pull request #6725 from brettp/ignore_reverts

fix(git): Igorning revert commits in Travis and in commit-message git hook