[Misc] Standardise naming of controller and service methods

[zsh-eng]

Currently, there are different names for the same kind of action in controllers and services, such as

edit vs update, create vs add.
We should standardise the verbs used for the controllers and services to avoid confusion.

• Create: create e.g. createUser
• List: findAll e.g. findAllVenues
• Get one: findOne e.g. findOneSubmission
• Update: update e.g. updateUser
• Delete: delete e.g. deleteUser