Add checking by html5validator

[php-coder]

We need checking our html templates with html5validator tool. At least in TravisCI.

@see https://github.com/svenkreiss/html5validator

[php-coder]

$ html5validator --root src/main/webapp/WEB-INF/views --show-warnings --ignore 'Attribute “(th|sec|togglz|xmlns):[a-z]+” not allowed' 'Attribute “(th|sec|togglz):[a-z]+” is not serializable' 'Attribute with the local name “xmlns:[a-z]+” is not serializable'; echo rc=$?
WARNING:html5validator.validator:"file:/home/coder/mystamps/src/main/webapp/WEB-INF/views/series/info.html":104.145-104.145: error: An “img” element must have an “alt” attribute, except under certain conditions. For details, consult guidance on providing text alternatives for images.
"file:/home/coder/mystamps/src/main/webapp/WEB-INF/views/series/add.html":127.35-127.35: error: Element “option” without attribute “label” must not be empty.
"file:/home/coder/mystamps/src/main/webapp/WEB-INF/views/series/add.html":149.35-149.35: error: Element “option” without attribute “label” must not be empty.
"file:/home/coder/mystamps/src/main/webapp/WEB-INF/views/category/info.html":15.124-15.124: error: Bad value “” for attribute “href” on element “link”: Must be non-empty.
"file:/home/coder/mystamps/src/main/webapp/WEB-INF/views/category/add.html":105.57-105.57: error: Attribute “path” not allowed on element “label” at this point.
"file:/home/coder/mystamps/src/main/webapp/WEB-INF/views/category/add.html":118.59-118.59: error: Attribute “path” not allowed on element “label” at this point.
"file:/home/coder/mystamps/src/main/webapp/WEB-INF/views/country/info.html":15.121-15.121: error: Bad value “” for attribute “href” on element “link”: Must be non-empty.
"file:/home/coder/mystamps/src/main/webapp/WEB-INF/views/country/add.html":105.57-105.57: error: Attribute “path” not allowed on element “label” at this point.
"file:/home/coder/mystamps/src/main/webapp/WEB-INF/views/country/add.html":118.59-118.59: error: Attribute “path” not allowed on element “label” at this point.
rc=9