Add support to log_timezones with + and - signs

pgbadger does not recognize log files (queries and events) with timezones like 'GMT+3'.

On postgresql.conf file the log_timezone variable is set as 'Etc/GMT+3' and lines are generated like this (stderr format):
2014-12-19 00:02:40 GMT+3 [1981]: [239-1] user=,db= LOG:  checkpoint starting: time