Function state mutability into dojo contract

[glihm]

Is your feature request related to a problem? Please describe.
Currently, all the functions of a dojo contracts (mostly systems) are generated as views. Even if dojo contracts are meant to be state less (we're not supposed to write any data into their storage), the ABI is then generated with state_mutability = view for those function.

Describe the solution you'd like
We should give the user the possibility to choose between view and external in the ABI, without having to pass ref self: ContractState or self: @ContractState.

In dojo, a system must be external if it writes data to the world storage. This is done using the set! macro. We should then inject the world with this information: ref world: IWorldDispatcher.

In the case we do need a view (to have some data returned from this view), we can omit the world injection, or inject it as it's done currently: world: IWorldDispatcher.