Fix space/tabulation in RrdDataFile.js
RrdDataFile: splitting fetch into fetch & build
RrdGraph: fix some indentation
RrdGraph.js: splitting RrdGraph.prototype.graph_paint into init, fetch and draw
RrdDataFile.js: Add async function (fetch_async) to RrdDataFile
RrdGraph.js: Add RrdGraph.prototype.graph_paint_async method
Change alter for thow
test async paint