Allow [[..]] filter notation in all text panels

Based on #408 with fixed filter service method. Supports html, text and
markdown panels.
Add diffSeries function support
Fix formatting negative values
Merge pull request #544 from Akeru/diffseries

Add diffSeries function support
Merge pull request #545 from Akeru/fix-format

Fix formatting negative values
updated change log with PR #545
Merge branch 'master' of github.com:Akeru/grafana into Akeru-master
Refactoring PR #511, Allow filter notation [[..]] in text panels
Fixed invalid references to grid.min and grid.max in function render_panel_as_graphite_png()
Merge pull request #550 from Fuitad/master

Fixed invalid references to grid.min and grid.max in function render_panel_as_graphite_png()
Refactoring influxdb datasource, split out response handling
added missing file from last commit
New legend display option 'Align as table' (Issue #136)
added y2 text after right y axis series, when legend is in table display mode #136
Enhanced InfluxDB series aliasing (legend names) with pattern replacements (Issue #525)
Some changes to influxdb alias pattern expansions, removed  as it was to confusion, added help text to influxdb metric editor view, need to polish a litle more, #525
Merge pull request #3 from grafana/master

Pull in Upstream Changes