save OPML export file with xml extension

The OPML importer doesn't accept ".opml", treating it as octet-stream.
fix auto language detection
Merge pull request #475 from hdhoang/patch-1

save OPML export file with xml extension
readme update
Merge branch 'master' of github.com:SSilence/selfoss
sources: show sources with error first
Sqlite's "optimize()" was implemented.
Merge pull request #478 from arbk/proto4optimize01

Sqlite's "optimize()" was implemented.
Merge pull request #477 from hdhoang/master

sources: show sources with error first
Merge branch 'master' of github.com:SSilence/selfoss
README.md updated
fix bug on base url determining using https
Support search terms with quotes to find exact phrase like "Windows 8"
Merge pull request #481 from gerundt/search-quotes

Support search terms with quotes to find exact phrase like "Windows 8"
readme.md updated
moved anonymizer functionality to helper
updated comment
Merge pull request #482 from bbeardsley/anonymizer-helper

moved anonymizer functionality to helper
use common file to init app (for index.php and update.php)
github spout: declare user-agent and more error logging

The GitHub API requires a user agent. This November change broke the Gihut
spout.

See http://developer.github.com/v3/#user-agent-required