This pull request addresses two issues by adding new shortcuts to comment fields.

Esc to blur comment field

When the user is inside an empty comment field and presses Esc the comment field will be unfocussed/"blurred".

Closes #848

Up to edit last comment

When the user is inside the "Leave a comment" field at the bottom of issues and presses Up while the field is empty, Refined GitHub will .click() the edit button of the last comment by the user and put the caret at the end of the input field.

Closes #858