first steps in copying css / javascript resources
initially created code frame for missing alt tags
started creating html tag selector method plus spec/test
nice methods: getAllImageTagsWithNonEmptyAltAttribute and getAllImageTagsWithMissingAltAttribute plus Specifications
formatting sources - trivial
refactored HTML_HEAD and HTML_END to its own class to achieve better DRY
some new convenience methods
another convenience method on HtmlElement
Missing alt attributes are now detected (no problem for asciidoctor, as it ALWAYS generates alt-attribute
Merge branch 'feature/#19-missing-alt-in-image-tags-checker' into develop

Conflicts:
	src/main/groovy/org/aim42/htmlsanitycheck/report/HtmlReporter.groovy