Use '/' keystroke for options search

[i2van]

Feature

Trigger options search on '/' keystroke.

Area

Game menu.

Motivation

Widely used UNIX search keystroke.

Workflow

Should be triggered when any menu is active and no editor is active.

1. Pressing '/' when any menu is active (and no editor is active) opens search options menu.
2. Option search proceeds as usual as if were initiated from menu.
3. Pressing 'ESC' returns to previously opened menu.