Correct Elev ID key passed by POST request

[engelsmann]

https://www.github.com/engelsmann/boxplot/tree/test_suite_1/templates%2Fboxplot%2Findex.html#L26

[engelsmann]

As of commit acaf2ca informal indications show that the ID is passed and compared correctly, but a formal, automated test needs to be formulated and carried out succesfully in order to close this.