[FEATURE] TypoScript setting with constant: gridColumns

Allows setting the @gridColumns LESS equivalent used by the CSS currently applied, if this value is not the default 12-grid. Can be set using a constant and can of course be overridden in the page tree.
[TASK] Bootstrap wrong in description

Just added the missing t.
Merge pull request #41 from NamelessCoder/typoscript

[FEATURE] TypoScript setting with constant: gridColumns