Settings: Split main settings view to tabs

[Taitava]

Currently, the main settings view contains the following settings:

• Working directory
• Shell commands
• Error message duration
• Notification message duration
• Preview variables in command palette
• A list of available variables (not actually settings, as there's nothing to configure).

76 will bring more settings to the main view:

• Macintosh default shell
• Linux default shell
• Windows default shell

These settings will be divided into different tabs.

• [x] Shell commands

  • The list of shell commands.
  • The list of variables.
  • Preview variables in command palette (until I come up with a better placement for this)

• [x] Operating systems & shells

  • Working directory
  • Macintosh default shell
  • Linux default shell
  • Windows default shell

• [x] Output

  • Error message duration
  • Notification message duration

Shell commands tab will be active by default, and it's the tab that a user will probably use more actively than the other tabs.

[FelipeRearden]

Great idea @Taitava :)

[Taitava]

This is how the main settings view looks after splitting to tabs:

(Icons will change to something else in the future, but that's a topic for another discussion.)

[FelipeRearden]

What a great new window @Taitava ! 👀 👀 👀 👀 👀 👀 👀

[Taitava]

Done & released.