added e2e tests for exporting student data

added instance export e2e test

Swapped Logout button and slot postion

Logout is now always a the far left

e2e tests are now using one browser instance per TestClass

Statistics endpoint now checks if there are submissiontypes available

Fixed race cond. in e2e test and bug in stats endpoint

Added function_tests to flake8 check

Added id "logout" to logout button

Using --cache-from in build step

Increased implicit wait for e2e test