* Add arrowhead support

As described in TODO, dotparser.js does not support 'arrowhead'
attribubte of edge.
This update is for adding 'dot' and 'tee'(bar) styles.

* Add example for arrow styles

* Add box arrowhead

To support box arrowhead of graphviz, add Box endpoint class in
EndPoints.js and box attribute in dotparser.js.

* Add diamond arrowhead

To support diamond arrowhead of graphviz, add Diamond endpoint
class in EndPoints.js and diamond attribute in dotparser.js.

* Add crow arrowhead

To support crow arrowhead of graphviz, add Crow endpoint
class in EndPoints.js and crow attribute in dotparser.js.

* Add normal arrowhead

To support normal arrowhead of graphviz, add Triangle endpoint
class in EndPoints.js and normal attribute in dotparser.js.

* Add curve arrowhead

To support curve arrowhead of graphviz, add Curve endpoint
class in EndPoints.js and curve attribute in dotparser.js.

* Add inverted curve arrowhead

To support inverted curve arrowhead of graphviz, add InvertedCurve
endpoint class in EndPoints.js and icurve attribute in
dotparser.js.

* Add vee arrowhead

To support vee arrowhead of graphviz, add Vee endpoint class in
EndPoints.js and vee attribute in dotparser.js.

* Add arrowhead examples

* Fix bug for accessing null attribute

In createEdge(), accessing 'attr' causes an error if the edge has no
attribute and the value is null.
This update fixes bug for accessing null 'attr'.

* Update description for arrows.to.type option

Add followingn options for 'arrows.to.type'.

* box
* crow
* curve
* diamond
* inv_curve
* triangle
* inv_triangle
* vee

* Update edgeStyle example for arrow types

Add arrow types for the example.

'box', 'crow', 'curve', 'inv_curve', 'diamond', 'triangle',
'inv_triangle', 'vee'

* background docs
* edge background
* Update edges.html
* Update EdgeBase.js

* Moved navbar elements in all html documentation files to partial

This consolidates the common menu elements in all documentation files to a partial.

* Moved test-exclamation mark

* Added partial, tested with some pages

* Docs: Moved end block in all html documentation files to partiel

This rcConsolidatersd common footer in all documentation files to a partial.

I'm hoping this serves as an example for others to isolate more common blocks (the menu would be the perfect candidate). It's straightforward work.

* Network: Adjust documentation for arrows.middle.scaleFactor

Addendum to #3474.

Updated the documentation, so that users can know about flipping the middle arrow with a negative scale factor.

* Adjusted text for review

* Add endpoint 'bar' to Network

Fixes #3412

- Adds class `Bar` and handling to `EndPoints.js`
- Adjusted `options.js` for endpoint, minor code changes
- Added to example `network/edgeTypes/arrowTypes`.
- Added to edges documentation

* Grumbl fix travis unit test yet again. Go die already!

* element characteristic changes
* assume edge color inheritance is correct before choosing
* Adjust nodes’ chosen’s boolean -> bool
* Need to get user-reset size
* make example edges thicker for more noticeable shadow
* preemptive ES6 fix (see #2500/#2501)
* documentation for the feature that was previously overwritten

* Multifont node and edge labels
* adjust documentation
* rework mod-font property inheritance
* Node max/min widths, min heights; Edge max widths
* Accumulate sizes correctly for unconstrained multipoint labels
* handle font.multi when groupOptions.font is not declared
* propagate label fonts on changes, not just creation
* Allow top-level constraint numbers
* accumulate width and empty lines appropriately

- Fixed #1528, #1278, avoided ID's being cast to string for methods that return ID's as well as storePositions casting to string.

see #909