[Feature] Remove iframe and embed from the focusables selector.

Reason: We use the focusables selector for 1) selecting the main element in a CU 2) for find-any-link. In both the cases, we don't need embeds and iframes to be focused (even though they are technically focusable). This is being done in response to an issue on Tumblr, where selecting CU focuses the iframe in it as the main element, and that breaks the scrolling flow (with j,k). Thsi is because all following key presses are caught by the iframe.
[Fix] A better fix for #!74.
We no longer apply inline-block to focused anchors that contain an image.
[Data] Add support for *.blogspot websites.
[Data] Improve FB main element data.

Remove workaround made for #174. No longer required because we've fixed the root issue.