fixes #1668 - added new options for allow column header insert / remove
TODO - tests tests tests
Merge branch 'develop' into feature/issue-1668

Conflicts:
	src/plugins/contextMenu.js
fixes #1668
merged develop + tests
fixes #1668
merged develop + tests
comments removed
Merge branch 'feature/issue-1668' into develop

Conflicts:
	dist/jquery.handsontable.css
	dist/jquery.handsontable.full.css
	dist/jquery.handsontable.full.js
	dist/jquery.handsontable.js
	src/plugins/contextMenu.js
	test/jasmine/SpecRunner.html
	test/jasmine/spec/Core_viewSpec.js