Add Search Bar Widget

[chand1012]

Adds a simple search bar widget that allows you to specify a search engine. Also adds the proper documentation for use. Closes #33.

[gitsang]

I compiled and test a version locally, is great.

But I would like to raise a few minor requests:

1. Can it automatically focus on the first search box? (Perhaps this should not be solved by the widget, I am not very familiar with frontend implementation.)
2. Is it possible to add a height adjustment option? Or support adding multiple search boxes in a single widget?

[gitsang]

Oh, and the query parameter doesn't seem to be working.

[svilenmarkov]

Hey, thanks for contributing!

I made a couple of changes and added a few more features, hope you like them!

PS: nice