Timezone correction across panels

This pull will help fix #95, #69, #70, #337, #340

* Timezone has been introduced in dashboard configuration. As this is the common setting to be used across panels viz. table, histogram and timepicker.
* In table configuration, added support to define timeformat
* From histogram removed timezone setting and pointed to use the dashboard one.
* In config.js, zone files can be specified which needs to be loaded.