URL bar hotlist indicator toggle

This is notice for frontend maintainers.

I've just added hotlist-add.png and hotlist-rmv.png icons to NetSurf's
default icons folder. They are intended for implementing a hotlist
indicator/button as seen on the right-hand side of the URL bars of the
other browsers these days.

hotlist-add.png -- Empty grey star outline.
Shows that current URL is not in hotlist.
Clicking adds current URL to hotlist.

hotlist-rmv.png -- Filled and coloured star.
Shows that current URL is in hotlist.
Clicking allows URL removal from hotlist.

The core hotlist module provides functions for implementing this:

bool hotlist_has_url(nsurl *url);
nserror hotlist_add_url(nsurl *url);
void hotlist_remove_url(nsurl *url);

Finally, the icons can either be loaded directly by frontend code, or
loaded via the content system. See the treeview module's content resource
loading for an example. Resource URLs for the icons are:

resource:icons/hotlist-add.png
resource:icons/hotlist-rmv.png

Cheers,

--

Michael Drake (tlsa) http://www.netsurf-browser.org/