External call semantics and interaction with service modules

[GraphR00t]

• External calls should no longer use the origin state, the caller's state and context should be used instead.
• The permissions of an origin state should be added to the caller's context and 'selected' each time the caller calls an external function coming from this state. This should be fast, at least for functions coming from modules of kind Unspecified and Library.
• How does limiters should work here ? It's important to note that increasing the complexity of external calls can have a significant impact and performance.
• Should interaction with services modules be achieveds using function calls ? Since services may be running in a different process, calls could be 'remote'.

Related: #38