Rework diagnostics

[rwols]

• Put the storage in the SessionBuffer class.
• Add delay setting.
• Add extra delay setting when the completion widget is visible
• Allow an empty string for the diagnostics style to suppress in-line
  diagnostics.
• Don't print a debug statement when a view is not found.
• Do not manipulate the diagnostics panel when another panel is visible.

Resolves #852
Resolves #858
Resolves #1089
Resolves #1155
Resolves #1130

This is still a WIP.

• Diagnostics panel functionality
• In-line diagnostics functionality
• Hover popup shows diagnostics
• Diagnostics cursor
• Diagnostic in status bar
• Figure out what to do with the project path prefix
• Test clearing diagnostics with "LSP: Clear Diagnostics" command (do we even need this?)

[rchl]

Maybe it's expected at this stage but just wanted to say that testing this with:

"diagnostics_delay": 2000,
"diagnostics_additional_delay_auto_complete": 1000,

and it seems quite erratic in that the diagnostics don't show for newly typed text that contains errors. I have to reopen the file for them to show up.

[rchl]

Test clearing diagnostics with "LSP: Clear Diagnostics" command (do we even need this?)

Kill it!

[rchl]

Maybe it's expected at this stage but just wanted to say that testing this with:

Oh, it's seconds, not milliseconds...

[rwols]

Oh, it's seconds, not milliseconds...

Yes. Perhaps that's too confusing? The other, existing "duration" settings are in milliseconds.

[rchl]

Then following existing convention would be better. And have _ms suffix for those.

[rwols]

Then following existing convention would be better. And have _ms suffix for those.

diagnostics_delay_ms is now in milliseconds, as well as diagnostics_additional_delay_auto_complete_ms. I've clarified in LSP.sublime-settings that the two are added together.

[rchl]

I think that this should be set to some decent value by default. Unless you feel that it's not finished or something (I haven't had a chance to try it out properly yet).