allow non-admin users to view plugin readme

fix(elasticsearch): for query template variable when looking up terms without query, no longer relies on elasticsearch default field, fixes #3887

fix(snapshots): fixed issue with viewing embedded/solo/png panel from snapshot without login, fixes #3769

fix(graphite): fixed minor graphite lexer issue when nodes begin with octal syntax and end with dash identifier, fixes #6049#

fix(templating): fixed issue with regex in query variable introduced by yesterdays big merged refactoring of template variable system