Automatic metals server installation

This release changes default metals sever command to use metals instead of metals-emacs.
lsp-metals will suggest to install metals server if it's not found.
A lot of improvements in metals integration.

Follow lsp-mode 7.0

• Migrate to lsp-protocol.
• Implement metals/windowStateDidChange notification.
• Drop emacs 25 support.

Migrate from lsp-mode

Migrate lsp-metals to a separated repository.