feat(omnibar): support initial query and enhance alias expansion

[twio142]

This PR adds two omnibar features:

• Initial query support for URLs type, and
• Improved alias expansion to only consider the part of input before cursor on spacebar press.

These two changes work together to allow opening the omnibar with a selection from page, move the cursor to the beginning, and type an alias to act on that selection.

It offers a different approach than having to specify one search alias with a key (i.e. sg).

api.mapkey('t', '#8Open a URL', () => {
  api.Front.openOmnibar({type: 'URLs', extra: window.getSelection().toString()});
});