Whitelist generation without broken dependencies

When generating a whitelist, checkbox-editor makes sure that some conditions are met to avoid breaking dependencies:

- When a test case is selected the test suite that contains it is selected as well.
- When a test case is selected all the test cases in the `depends` field are also selected.
- When a test case is deselected, the test suite that contains the test case is deselected if no other jobs are selected.
- When a test case is deselected, any reverse dependencies (test cases depending on the test case being deselected) are deselected as well.

However, there are a couple of things regarding ordering that could be improved to get whitelists that don't need to be reordered when checkbox is executed:
- Resource jobs should always be at the top of the whitelist
- Dependencies that are found in different test suites aren't automatically selected and that can be used to generate whitelists with wrong ordering.

For example, when clicking on `keys/sleep` test, `suspend/suspend_advanced` isn't selected. Besides this, if `suspend/suspend_advanced` is selected later, then it's appended to the whitelist even though `keys/sleep` test depends on it and this generates a wrongly ordered whitelist.