adds sort order to API

Allows sort by feed date or by reverse order
api Params:
order_by (string = feed_dates, date_reverse)
move HOOK_TOOLBAR_BUTTON elements inside actionChooser
make show empty cats menu item more visible, move unsubscribe to feeds dropdown
add optional support for the X-Sendfile header
opml: add some data length limiting
Merge pull request #117 from j0nson/patch-1

add sort order to API getHeadlines
Revert "add php native gzdecode()"

This reverts commit f2c624a23640eb1e47d83842d0bf8303209155b6.
import_export: fix syntax error, adapt to work with new gettext syntax
Merge pull request #118 from vapier/x-sendfile

add optional support for the X-Sendfile header
api: add a few logical spaces
af_redditimgur: insert br after image
update 'no articles in label' hint
Add hook to add explanations of hotkey actions via plugins.
Merge branch 'master' of git://github.com/gothfox/Tiny-Tiny-RSS
installer: mention lack of curl
sessions: initialize connection on include, not in ttrss_open
initialize session connection in ttrss_open but define session_connection in global context
instances: fix a few wrong calls, move genHash method from rpc
remove some old ?op syntax notation calls
move batchAddFeeds to pref-feeds