[Proposal] CSS needs a top selector

[ramezrafla]

Right now the CSS file assumes you have only SocialCalc (or at least majorly SocialCalc) in your app. We need to add SocialCalc-specific class the container:

For example, start with:

<div id="mySheet"></div>

And then call

var socialCalcControl = new SocialCalc.SpreadsheetControl()
socialCalcControl.InitializeSpreadsheetControl(document.getElementById('mySheet'));
SocialCalc.SetTab("edit");

Which would add class sheet to that div

<div id="mySheet" class="sheet"></div>

So the CSS file needs to have all selectors preceded with .sheet (or something constant)