docs(code): merge coding_standards into contribute/code.rst
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
docs(performance): add suggestions for performance and scalability
Merge pull request #6728 from ewinslow/docs-performance

docs(performance): add suggestions for performance and scalability
Merge pull request #6705 from juho-jaakkola/generic_upgrade_view

Generic XHR upgrade features