Enable comparison view of multiple failed tests (in the same file)

[mmews-n4]

Before, it was possible to see a comparison view that showed all failed expectations of one file. This view was handy because one could copy all actual results and paste them into the xt-file in order to fix all tests. Now, this is not possible and instead, one has to do that for every failed expectation manually.

Note that the button "Compare Actual With Expected Test Result" is greyed out when the file is marked in the JUnit view. This should be reactivated.