Fixed Toolbar: removing popup removes ui-page-header-fixed class

Fixes #6987
Fixes #6939
Rather then looking for pageActive here lets add a reference to the pagecontainer in create. we can then reuse this to get the active page when ever we need it. 
```
// For now we can just take the first pagecontainer as we only support one this will change in the future
this.pagecontainer = $( ":mobile-pagecontainer" )[0];
```
Then anywhere we need to check the active page we can just do 

```
this.pagecontainer.pagecontainer( "getActivePage" );
```
then we have a reference with out querying the DOM much faster and less error prone and no need to check length or look for `.ui-page` as it will always be set.