Add support for --jsonrpc-apis all

[chevdor]

It would be nice to be able to use:
parity --jsonrpc-apis all

with all being the entire list of available apis.

[tomusdrw]

Great idea!
I'll implement sth like this:

• all - All APIs exposed (warning should be printed)
• readonly - Read only APIs exposed (safe APIs)

and maybe additional syntax for:

• all,-parity_accounts - All APIS without parity_accounts

[chevdor]

@tomusdrw readonly and the -api features would definitely be a cool extra to all!

In the context of --chain dev, it would make it convenient, as you mentioned, to have things like all,-parity_accounts to start quicker.

safeonly may be a better name than readonly since you felt the need to explain that read only APIs are the safe ones.