Allow HTTP authentication without password.

This makes it the plugin useful for any form of webserver-based
authentication (CAS, SAML, etc.); of course, other plugins will
have to be installed to handle connections to the IMAP/SMTP
servers, but at least they don't need to duplicate the basic
HTTP authentication functionality.
style for focused messages
Merge remote-tracking branch 'upstream/master' into row-focus
tiny-focus column for determining where focus should be
Merge remote branch 'upstream/master' into row-focus
Small performance improvements, use str_replace() instead of strtr(),
do not parse query if there are no params to replace,
keep one instance of (potentially long) query less in memory
Move focus column to the left-most side
fixed some whitespace stuff
Avoid rcube_session::reload() to reset previous changes. This fixes parallel attachment uploads that could get lost when using the database_attachments plugin
Merge branch 'master' of github.com:roundcube/roundcubemail
Better handling of fopen() errors
Fix operations on folders with trailing spaces in name (#1489419)
Fix archive button state (i.e. checking if current folder is archive folder)
Fix categories/groups import from csv
Substitute variables in 'password_ldap_search_base' value
Add filetype icons for Powerpoint and Openoffice Presentations (#1489225)
Merge pull request #141 from rasky/http_without_pwd

Allow HTTP authentication without password.
Finish advanced prefs feature (#1488829)
Merge branch 'master' of github.com:roundcube/roundcubemail
Adjust date column size to fit the widest possible date format (#1489368)