Once again fix Czech translation

Signed-off-by: Frca <killerfrca@gmail.com>
Update view when registered on/logged of an exam

Signed-off-by: Frca <killerfrca@gmail.com>
Fix crash with classmatates loaded when fragment is already gone

Signed-off-by: Frca <killerfrca@gmail.com>
Use own executor for executing tasks

Signed-off-by: Frca <killerfrca@gmail.com>
Add Slovak translation and minor changes to Czech translation

Signed-off-by: Frca <killerfrca@gmail.com>