Initial commit.

Implement the basic images downloading functionality from molotok.ru website.
The tool is supposed to be useful for collectioners who would like to
investigate circulation periods of postal stamps and postcards. Downloading
items images manually is complicated and takes time. The plugin simplifies
that by downloading all related to item images in original size in one click.
Add options page.

The options page allows to set a relative path where to save the files. The
path is relative to default download location set in Chrome. If not specified,
the Chrome default path will be used instead.
Move download link styles to the separate css.
Fix empty filename parameter issue.
Minor coding style changes.
Rename styles.css to options.css

To reflect part of extension it belongs to.
Re-populate links after dynamic change of the page content.

Page or sorting order change results in page dynamic reload via AJAX call.
Once the new content is displayed, it is needed to re-populate the download
links.
Stop checking mutation.type.

It is always the same at the moment.
Add listener to offer preview window download link.
Only populate links on search results listing page.

Item details page has different layout, so the link adding process will be
different. At this stage we add download link to search result listing only.
Add license and readme files, copyright and licence statements.
Change extension description in manifest.