Add default timezone when system one is missing

Suppresses all the PHP warnings in the error logging.
Merge pull request #38 from oohlaf/timezone

Add default timezone when system one is missing
automatic page refresh support + config setting

Closes: https://github.com/pommi/CGP/pull/35
fix heigth -> height typo
graph: add configurable limit to graph width/height

Closes: https://github.com/pommi/CGP/pull/34
plugin/tail: collectd < 5 backwards compatibility

Closes: https://github.com/pommi/CGP/issues/36