Less version of bootstrap + Bug FIx: top bar on small screen

[axyz]

margin fixed to avoid the top bar to slide down leaving a blank space at his top when the window is small

I've also made a major change: by default use the less version of bootstrap in order to change in realtime variables.less

P.S. maybe i had to divide these commits in 2 branches because the bugfix is just a minor fix, while the less version of bootstrap is a big difference and maybe there are some serious reasons if you decided not to use it.

I'm sorry but i'm new to pull requests and i didn't know that new changes i made to a branch are also added to the open pull requests.

[balupton]

You should have received an invite to join the DocPad Extras Team, which will give you write access to this repository, so you can merge in the PR. I am too preoccupied to review it.

For an orientation, or if you need any assistance following the semi-automatic release process from CONTRIBUTING.md, then reach out via https://bevry.me/discord/dev