Replace main with auto language client.

Things that are working:
- go to definition
- hover (gopls supports signature only for now, no documentation)
- completion
- diagnostics
- signature help

Things that don't work:
- code highlight (needs troubleshooting)
- formatting (gopls sends error)
- outline view (unimplemented in gopls)
- organize imports action (atom-ide-ui requires a corresponding 
diagnostic)
- references (not implemented in gopls)
- rename (not implemented in gopls)

Functionality not included in LSP that needs to be restored from 
previous main:
- Go-plus panel
- implements
- Build/test on save
- Diagnostics from additional linters
- Implements Query
- Add import dropdown
- Info tab
- Struct tags support
- Code coverage