fix(gantt): Smooth gantt initialization and rendering

Columns are first generated after rendering in a $timeout. It allows to build columns when the global layout of gantt is already performed by the browser. At this time, labels width is available.

Before those changes, columns were flickering at init time because. Columns were generated at wrong size the first time because labels column was still not rendered, and resized after labels column display.

This also enhance scrolling by dropping gantt-limit-updater, fix an issue on wide screens at first loading, and another issue for labels having 0px width when loading data on a existing empty gantt.

A new api.core.on.rendered was added, raised when gantt if fully rendered on display after columns generation.

Close #223