Merge branch 'tsdb_downsample' of https://github.com/frogmaster/grafana into frogmaster-tsdb_downsample

Panel: Different time periods, panels can override dashboard relative time and/or add a time shift, #171, only works for graph panel for now, need feedback for how to do it for singlestat panel

Began work on time overrides for panels, to enable different time periods on the same dashboard, #171

Timepicker: New option in timepicker (under dashboard settings), to change now to be for example now-1m, usefull when you want to ignore last minute because it contains incomplete data, Closes #1242, Closes #374

Graph: Fix for all series tooltip showing series with all null values when Hide Empty option is enabled, Fixes #1359

TemplatOCing: Fix to allow custom template variables to contain white space, now only splits on ',', Fixes #1363

Graphite: Fix for nested complex queries, where a query references a query that references another query (ie the #[A-Z] syntax), Fixes #1372

Fixed asteric icon in graphite metric path selector, broken after resent font awesome upgrade, #1361

Graph & Singlestat: New axis/unit format selector and more units (kbytes, Joule, Watt, eV), and new design for graph axis & grid tab and single stat options tab views, #1331

Added new units to dropdown in singlestat options, need to add new unit selector to singlestat panel, #1331