simplify locales

Author:    Claudio Canepa <ccanepacc@gmail.com>
updatet .travis.yml to support two locales - eliminated abreviations in imports
compat 2.x in locale linux codepath
test_rss_feeds initializes LocaleBorg in setUp
LocaleBorg services as instance methods to ensure initialization
reshaping paranoid damage control forcalendar in windows
allow configure which locales in testing with environmet variables NIKOLA_LOCALE_DEFAULT and NIKOLA_LOCALE_OTHER
update changelog
addresed kw review
fixed remaining _linux -> _posix
flake8; fix #841 (the actual errors are to be handled somewhere else)

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
Fix tests
Include XML in GZIP_EXTENSIONS (for RSS, sitemap)

Resolves #844
Add a note about rebasing to CONTRIBUTING.rst
Merge pull request #845 from getnikola/config-compress-xml

Include XML in GZIP_EXTENSIONS (for RSS, sitemap)
add .xml to default config (via 87b0bde)

Thanks @punchagan
Merge pull request #818 from ccanepa/better-locale

simplify locales
merge
make docstring a bit more generic
Merge branch 'refactor_post_rendering' of github.com:getnikola/nikola into refactor_post_rendering