Setup nvim lsp

[lasse16]

One main feature of neovim over vim is its builtin LSP-support. In this PR, I set up nvim and the builtin LSP.

There are multiple subfeatures in this PR, like :

• Rust-Analyzer integration
• Popup window border and highlighting
• Diagnostics/Linting
• ALE Integration
• Snippet integration
• Completion via LSP