LSP: module based Autocompletion and Hovers

[vknabel]

Our language server needs correct autocompletion, that works across file bounds. Instead it should parse the whole module structure including all imports.
The autocompletions and hovers should only respect current imports.
Both should not rely on type inference, yet.

These cases should be supported:

• import members of a module, like lists.append
• global and local declarations (func, let, enum, data, extern)
• parameters