Add keyboard navigation.

[mikhin]

Fix #559, fix #521.

Hi! First of all I want to thank you for this package – it does really cool job.

My motivation to create this PR (quote from https://webaim.org/techniques/keyboard/):

Keyboard accessibility is one of the most important aspects of web accessibility. Many users with motor disabilities rely on a keyboard. Some people have tremors which don't allow for fine muscle control. Others have little or no use of their hands, or no hands at all. In addition to traditional keyboards, some users may use modified keyboards or other hardware that mimics the functionality of a keyboard. Blind users also typically use a keyboard for navigation. Users without disabilities may use a keyboard for navigation because of preference or efficiency.

So, in this PR I have added these features:

• Navigate through providers via keyboard;
• Close modal via ESC.

If you will see something that could be better, please feel free to make a comment.