Add ability to highlight text

[dshemin]

Story:
As an authorized user, I should be able to select part of the PDF document and mark it with some title and note.

How:
User should select a part of text and press "h" button. Modal window should be shown with two inputs:

1. For title
2. For note (optional)

And user should see two buttons:

1. Cancel
2. Create

On "Cancel" button, modal window should close and no highlight should be created.
On "Create" button, modal window should close and new highlight should be created.