change label to URL (instead of host)

- protocol is always required

Related to #16
refactor: use static gson instance
refactoring (sync some updated from intellij github plugin)

- http handling (support new methods, use head request for login, use stream instead of string for json parsing)
- logging (use same logger for all classes)
- self signed cert message box
set accept header for faster processing

- as suggested by Gerrit
- refactor: introduce constants for often used strings
fix timezone handling

- Gerrit uses UTC
minor cleanups
improve exception handling
add test for parsing change infos

- also test date parsing (eg. time zone)
add support for https servers on non-default port with self-signed certs
handle X-Gerrit-Auth http header

- pass header with following request when successfully logged in with /login url
fix showing file comments (not attached to a line)

- show them on first line (better than fail)
update login information note
Merge remote-tracking branch 'remotes/origin/master' into intellij13