Write all item fields as data-? attributes on element

If the dataAttributes config option = 'all' then write every field as
data-? attributes on the element.
Update examples to include all_data_attributes
Updated dataAttributes documentation for 'all' option
fixed node label becoming undefined
fixed cluster sector scaling
fixed cluster font scaling
updated history
updated constructors for timeline and graph2d (container, items, groups, options) with backwards compatibility
updated background itemtype. No content is allowed now.
updated docs and examples with new constructors.
no default padding and margin for backgrounditems
Simplified the background item support for empty/undefined contents
Fixed height of BackgroundItems not being 100% when timeline has a fixed height
tweaked graph2d based on timeline. Introduced ignoreStacking for items, used in background item type.
Merge pull request #340 from fabriziofortino/develop

graph3d: added support for custom axis ticks labels
Updated history and docs
Fixed some typos in the docs
Merge pull request #327 from dturkenk/all_data_attributes

Write all item fields as data- attributes
fixed missing this