Latte: implement better detection of HTML tags in HtmlNode

[dg]

To aviod these workarounds:

nette/Nette/Latte/Macros/FormMacros.php

Line 194 in 8559b78

preg_match('#(^.*?>)(.*)(<.*\z)#s', $node->content, $parts);

nette/Nette/Latte/Macros/UIMacros.php

Line 306 in 8559b78

&& preg_match('#^.*? n:\w+>\n?#s', $node->content, $m1) && preg_match('#[ \t]*<[^<]+\z#s', $node->content, $m2)

See http://forum.nette.org/en/1327-nette-2-1-0-stable-issue-with-form-n-name-macro-and-other-macros-in-html-attributes