Multi crate workaround dialog

[alexheretic]

This pr eases the current issues with multi-crate projects by offering workarounds with minimum effort.

Example

rls-1202/
├── project-bar
│   ├── Cargo.toml
│   └── src
│       └── main.rs
└── project-foo
    ├── Cargo.toml
    └── src
        └── lib.rs

If you open rls-1202 as a project in atom RLS will fail to find the root manifest and won't work.

A decent workaround it to add a root workspace manifest.

[workspace]
members = ["project-bar", "project-foo"]

With this RLS can work compiling everything and using a single root ./target directory.

You may also want to ignore the project and do without RLS functionality. This PR adds both workarounds as clickable actions when it can detect them.

Resolves #69