Fix the bug of subjects alloted to teachers

[Chirag4904]

Once the teacher is assigned a subject it is stored in alloted Subject array so if the subject is removed from that teacher then the hours are updated to 0 but the object still remains in alloted subjects which is taken by ui and displayed.

[Chirag4904]

@RoguedBear I am wondering if it should be handled in frontend or backend. In frontend side I can just add additional checks if all L,T,P hours are equal to 0 then it will not be displayed. Alternatively if in the backend we check if the L,T,P becomes 0 for that alloted subject then that subject should be removed from the allotedSubjects array for that teacher. What do you think?

[RoguedBear]

ideally this should be handled in the backend, when you call the delete teacher api or when the ltp hours reach 0 for a manually added teacher, the backend takes care of all the places to delete that teacher from

[Chirag4904]

Ok let's see if it's too much hassle for now then we will do it in frontend and keep this issue open otherwise fix it in the backend.

[RoguedBear]

completed in #106