Allows you to zoom and pan now.

relates to #647

fixes #439
Workaround for https://bugreports.qt.io/browse/QTBUG-97401
fixes #810

- If an inline image has specified a height, add parameters to the
  image:// URI.
- Add scaled to the parameters, the images would be cropped otherwise.
- Extract the height from image:// URI and use it for requestSize.
- Use scaledToHeight instead of scaled.

fixes #435

fixes #519

This warns when you the return value of those functions isn't used.

Suggested-by: Clang-Tidy: Function X should be marked [[nodiscard]]

Suggested-By:

Clang-Tidy: Single-argument constructors must be marked explicit to
avoid unintentional implicit conversions

More info: https://clang.llvm.org/extra/clang-tidy/checks/google-explicit-constructor.html

Suggested-by:

Clang-Tidy: The 'empty' method should be used to check for emptiness instead of 'size'