Replace image-size lib with custom code for reading PNG metadata

This removes the dependency on Node's buffer type in favor
of typed arrays for consistency with other code.
Output the name of the test when starting a suite

This makes it possible to identify which test suite failed
if one suite in a series fails due to an exception.
Prepend '/' to paths before issuing request in http.Client
WIP - Partially working display of fetched icons in app
Pick smallest icon larger than the preferred image size for the item overview list