We only have a good HQ source for them; any idea on a low-quality
source?

Should fix #412

Cockatrice can now load images both with and without .full. Will need to clean-up bool stripped (used to determine .full suffix inclusion).

I should probably bust this out to a method.

Cherry-picked b9cb61abd05f83c67740aafa5e1e6939143547e4

Like M15’s .png that cockatrice wrongly saved as .jpg
Additionally, move the QImageReader declaration outside of the inner
loop

Removed the QLists for determining image format. Instead, using QImageReader, both when downloading/saving and when loading, to determine the correct format (Cockatrice now supports all QImageReader-supported formats).
Image loading still uses one for loop to iterate through the QList of paths to folders in which to search for images.

Refactored the magic bytes into two QLists: one containing a list of QStrings representing the supported extensions, the other containing a list of QByteArrays representing the magic bytes in hex.
Refactored the image loading loop to be two nested for loops: the outer loop iterating through the QList of paths to folders in which to search for images and the inner loop iterating through the QList of supported extensions.

Switched back to using QFile instead of QImage for saving as QImage's save function adds overhead to the file size, leaving me unsure whether the original image is affected.

So [card]jotun grunt[/card] works as well as [card]Jötun Grunt[/card].
Also I removed some debugging information I accidentally left in.

Added better support for custom card images by prioritizing a check for card images in <Pictures path>/<CUSTOM> before all other checks.

Ref #127

Ref #122

Better error message and allow the user to still connect

Ref: #102