rename getConfig -> getProjectConfig, make all linters use getConfigFromAnySource

Summary:
Lingers on from D7271; Rename `ArcanistWorkingCopyIdentity.getConfig()`.

Changed all linters (Except one) to use `getConfigFromAnySource()`, because it seems to make sense.

Test Plan: arc unit --everything; arc lint in github.com:epriestley/arclint-examples.git (Except for phpcs, flake8, cpplint and csslint which I don't have installed).

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley

CC: chad, Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D7382