chore(contributing): Add branching guidelines

Close #173
refactor(columns): Use momentjs for column handling

This is a big refactor in column handling using momentJS features.

view-scale now supports any of momentJS unit, like year, quarter and minute.

headers-* options have been dropped, in favor of headers and headersFormats (see README).

This drops support of everything related to working hours, weekends and column-sub-scale. Those options will be replaced by #126 and #123.

Close #79
feature(calendar): Add calendar factory

This add the calendar factory, to support configuration of timeFrame, dateFrame and timeFrameMapping.

This is the primary step for "#126 Global definition of non working periods", and implements draft from gist https://gist.github.com/Toilal/5871680f0e5f2fa54412.

This also adds the first unit tests, using karma, jasmine and phantomJS, integrated in grunt default task.