v5.7: add toolbar icons, select JSON from tree, major RemesPath improvements

[5.7.0] - 2023-09-08

Added

1. Toolbar icons for JSON pretty-print, JSON compress, treeview, and path to current position. Fix issue 36.
2. Ability to select JSON or a JSON's children from the treeview.
3. Variable assignment in RemesPath.
4. Negated indexers in RemesPath.
5. Ability to group by multiple variables with the group_by RemesPath function.
6. Option to skip the API request test when running tests.

Changed

1. Selections that don't begin with a valid JSON document will now be ignored when parsing a document. See working with selections docs for more info and examples.

Fixed

1. Sort form previously did not follow Notepad++ styling on startup.
2. Problems (introduced in v5.5) with running tests multiple times without cleaning up test files.