Harden WebAssembly by allowing it to be used only through permission

[david0xd]

Because of the complexity of the WebAssembly endowment additional hardening is required.

Hardening WebAssembly endowment will include:

• Removing the WebAssembly from default endowments.
• Create a new permission endowment:webassembly which adds access to it.
• Make the endowment:webassembly only usable in Flask.