don't log people out just because the connection to server failed

fixes #278
strip password from api exception message

the underlying exceptions might still have the complete url in their message, though, but that's acceptable for now
fixes #261
make search button less awkward

fixes #273
prevent empty fields from collapsing the message view

fixes #271
Merge git://github.com/Graylog2/graylog2-web-interface into develop