Initial bulk of viewport overhaul

Relates to #98, #117, #89, #106.

This is the first stage of the overhaul described in #98.  The goal with
this commit is to basically make PD minimally functional again, but
using a custom "canvas" user control instead of standalone windows for
displaying and interacting with images.

I haven't tried compiling this commit, but you can run the software from
the IDE and do basic image edit tasks.  Many more commits will be
incoming as I do more detailed testing...
Fix canvas background color when changed from Options dialog
Fix run-time errors if clicking on the canvas while an image is unloading
Fix Curves dialog presets to account for comma as a potential decimal separator in some locales
Remove redundant "preview" label in autosave dialog
Change various Print # to Write # to prevent locale-specific changes
Get program compiling again

Also, undo previous Print/Write swaps - this introduced undesirable
quotation mark behavior and destroyed all XML parsing.
Remove now unnecessary WindowState tracker in pdImage
Fix listbox order problem on Autosave dialog
Fix additional locale issues in Curves dialog when saving/loading presets
Fix erroneous image unload behavior
Clear canvas user control when program first starts
Fix floating toolbars appearing over Save common dialog

Fixes #117
Resize the main form's canvas when the image tabstrip is resized
When the current image thumbnail lies off-screen, bring it back on-screen
Change various CDbl() to CDblCustom() to better handle locale differences

Inexplicable errors from Italian users lead me to believe there are
inconsistencies with various VB functions' handling of locality when
parsing floating-point strings.  To try and negate this, I've written a
simple CDblCustom() function that will accept comma or period
separators.
Get progress bar working again
Remove standalone Image form from repo

This form has been part of PD since the beginning - farewell, old
friend!
Update official Italian language file

Many thanks to GioRock for the translation!
Fix translation generator to process controls with "Shape" in their name