Render nodes as real links

[flying-sheep]

Fixes #689.

I think we should replicate the HTML label behavior manually instead of relying on dagre-d3-renderer (i.e. if labelTypeStr === 'html', we create a foreignObject ourselves and pass it to the library).

That way we can wrap the whole thing in a SVG <a>...</a> object instead of only having the narrow link text clickable.

[coveralls]

Pull Request Test Coverage Report for Build 701

• 9 of 28 (32.14%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.0005%) to 54.285%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/diagrams/flowchart/flowRenderer.js	0	8	0.0%
src/diagrams/flowchart/flowDb.js	5	16	31.25%

Totals
Change from base Build 671:	-0.0005%
Covered Lines:	2049
Relevant Lines:	3752

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💛 - Coveralls