Username normalization on login

[Paktosan]

Some users try to set a username with capital letters during registration. When they try to login into SIPA, they get "Wrong credentials" because they did not write their login in lower case letters. I would propose that we set every letter lower case before checking the login.

[ibot3]

Cannot reproduce.

[lukasjuhrich]

@ibot3 Please provide more information. Do you mean to imply that the sipa login already is case-insensitive? Because skimming through the code, we nowhere issue a call to .lower().