Update html templates markup to follow h5bp. Closes #20

[peterblazejewicz]

This PR refactors markup used in header of the html pages templates to follow advices from @h5bp project:
https://github.com/h5bp/html5-boilerplate/blob/master/src/index.html
Additional feature of this PR is to bring compatibility with @bootstrap project @bootlint tool - as MVC templates tend to use that framework frequently - this will remove some work from users of templates hopefully :D.

[sayedihashimi]

@peterblazejewicz thanks for the PR. Should we provide a default value of en for lang? The template has English content so I think it would make sense.

[peterblazejewicz]

@sayedihashimi there are lengthy threads on h5bp why lang should be included in boilerplate contents and why should be empty:
h5bp/html5-boilerplate#1542
Having this attribute will respect system settings at least (as per discussion). I don't think that content is in English - the boilerplate content is English based only - but it is assumed to be removed/changed by end-user like me.
For example Google's Web Starter Kit is written in entirety in English but does not specify it's content lang attribute:
https://github.com/google/web-starter-kit/blob/master/app/index.html#L2

[sayedihashimi]

@peterblazejewicz sounds good, I've merged it. Thanks.

cc @rustd