PDF improvements and more

- Removed dependency of some macoslib methods on StringExtensions or DebugReport.

- Rebased PDFView on CanvasForNSView.
- Implemented events to PDFView from NSNotifications: DocumentChanged, PageChanged, ScaleChanged, SelectionChanged, HistoryChanged, DisplayModeChanged.
- NSObject: added Superclass and PerformSelectorOnMainThread (untested).
- Enabled the close widget of the Welcome to macoslib window. Window can be opened from the Help menu.

- Cleaned unwanted commented-out code
- Reverted the previous commit, as nobody liked it :-(
- Added PDFView and PDFThumbnailView which work together to display, edit and print a PDFDocument.
- Display of built-in PDFs is now using the "single-page continuous" option and has a thumbnail view. As such, they can be printed without any code !
- Documented PDFView and PDFThumbnailView.
- Created a CanvasForNSView object to serve as a parent class for all NSView subclasses using a Canvas at the Xojo level.

- Created module macoslib_32_64bits_savviness in Misc. folder to hold 64bits compatibility functions:
    - SizeOfInteger and SizeOfPointer return the size of an Integer or a Pointer.
    - bsPtrValueFromCArray, bsIntegerValueFromCArray return a Ptr or Integer in 32/64 bits given a C-Array index.
    - bsPtrValue, bsIntegerValue return a Ptr or Integer in 32/64 bits given the offset.
- Methods using SizeOfPointer now raise a warning at compilation time. This could be improved later.
- Stripped off most of my dead code. For work in progress, made clearer why some code is commented out, per TT's recommendation.
- Set "FPtr" function as a global function in the new macoslibModule and removed multiple definitions of it as Shared Methods.
- For CanvasForNSView, created a LoadRequiredFrameworks which will ask for and load all the required frameworks. It can be called several times and returns more quickly than RequireFramework.