Add model for threshold info that can be used to show custom threshold lines on fews objects graphs.
PEP8 changes
Merge branch 'master' into thresholds
Remove obsolete piece of code
Put threshold line on graph if threshold data is available
Update CHANGES.rst
PEP8 fixes
Remove obsolete function
Add threshold views.
Update CHANGES.rst
Fix html form
Update dutch translations
Update dutch translations
Derive threshold line color from identifier line color
Improve look and feel
Merge branch 'master' into thresholds