keep the grid overlay on as you navigate from page to page and/or ref…

[denisinvader]

#61

Use cases

• User enables the grid (and/or horizontal lines) overlay. User refreshes the page. After the page refresh the grid (and/or horizontal lines) overlay is rendering automatically;
• User enables the grid (and/or horizontal lines) overlay. User opens a new URL (by link or directly input) in current tab. After the page refresh the grid (and/or horizontal lines) overlay is rendering automatically.

It don't work

• When user follows the targer="_blank" link (which opens in a new tab);
• When user use extension in local file (the file:// protocol). It's necessary to use web server. (Chrome web server will work fine).

Issues

• Add keypress listener in content_script and let user use keyboard shortcuts without opening the popup (enhancement);
• After a page refresh, when the grid overlay is rendered with non-default options, if user opens the popup, options set to default and the grid re-renders with default options.

[denisinvader]

Also fixed double grid overlaying