Provide description of structure of test marks in pcs-web-ui.

The description should be in document in json format. This document should be distributed as a part pcs-web-ui similarly to manifest.json. So, it would be possible to download this document from url similar to e.g. https://node:2224/ui/manifest-test-marks.json

The test marks are represented by attributes data-test of html elements of the page. Inside element marked like this can be nested html structure with another elements also marked by data-test. This way the marks creates tree-like structure.

In the mentioned json document, this structure should be represented by a json object. Keys of this object corresponds to the values of the top level data-test attributes and the values on the keys are objects (similar to top level object) representing the corresponding nested html structure.