Settings: Search field for Variables tab

[Taitava]

The list of custom variables - while short in the example above - can grow long. Also, the list of builtin variables below it is quite long.

I'd like to add a search field (above Custom variables heading and below Show autocomplete menu setting) that would filter both custom and builtin variables.

Searchable properties for custom variables:

• Variable name, including {{_ and }}.
• Description
• Default value (will be introduced in version 0.18.0). Just the freeform value part of it.

Searchable properties for builtin variables:

• Variable name, including {{ and }}.
• Description
• Default value (will be introduced in version 0.18.0). Just the freeform value part of it.

[Taitava]

Add a search field to the extra options modal, too