PRD-3833 - Drilldown to another report opens in same tab showing Report Parameter panel of both reports.

Apart from the following commit change log, there's one thing I'm not sure to be doing right. I added a new file "reportviewer-logging.js" and it is being requested using pen.require in reportviewer.html. Anyway, there, there is complex logic for loading compressed vs uncompressed code. I have not registered the new file in reportviewer-app.js or reportviewer-main-module.js, because, honestly, I don't quite understand how this works yet.

##### Commit change log
* Removed some unnecessary viewer.view.resize calls.
* Removed some unnecessary viewer.view._showReportContent calls.
* Added logging to enable debugging in iOS/Safari.
  Inspecting url "debug=true" to activate logging.
  Added new file to support this: reportviewer-logging.js.
* Changed most JavaScript calls to set element Styles to setting Classes.
  Added new classes to body to support this: contentHidden, topViewer, leafViewer, parentViewer, mobile, nonMobile, nonStyled and debug.
  All styling is now done in CSS.
* Fixed a bug in which the prompt panel would be unavailable instead of collapsed by default.
* Renamed viewer.view.resize -> viewer.view.resizeContentArea and of viewer.view.resizeIFrame -> viewer.view.resize (full resize, includes the former)
* Renamed viewer.view.updatePageStyling -> viewer.view.setPageStyled
* Fixed the iOS scrolling hack (in viewer.view._resizeMobileHtmlReportHandlesScrolling) 
  being incorrectly applied to a child report viewer, messing the layout.
  Now checks if the child report is a report engine report by looking at the meta[@generator] attribute.
* Added a check that prevents styled content to be too small, by assuming a default width of 2/3 of viewport.width.
* Added detection of "unrequested" content iframe loads. This can happen because of links in the html content (viewer.view._updatedIFrameSrc).
* Removed the local viewer.view.isPentahoMobileEnv() predicate and started using the global "inMobile" variable, just like with other similar global indicators.
* When the content is a child report viewer, changes to non-styled.
* Fixed styled report not being centered in IE8.
  Now using #reportPageOutline {display:inline-block} and #reportArea{text-align:center} instead of #reportPageOutline{ margin-left/right:auto }.
* Removed unnecessary language="javascript" attributes from script tags.
* Added global variables _isReportViewer and _isTopReportViewer to facilitate testing for child report viewers.