Support for negative thresholds.
Merge pull request #1140 from johnou/support_negative_thresholds

Support for threshold colouring of zero / negative values.
SinglestatPanel: Fixed absolute drilldown link issue, Fixes #1150
Tech: updated angular libs
Firefox: Workaround for Firefox bug, casued input text fields to not be selectable and not have placeable cursor, Fixes #1123
Templating: added validation to template editor for variable names, Fixes #1133
Templating: added validation for allowed characters in variable names, Closes #1106
Graph: Fix for tooltip series order when series draw order was changed with zindex property, Fixes #1108
Annotations: added html sanitation to prevent markup injection/XSS, Closes #1121
Merge remote-tracking branch 'upstream/master'