Smarter embed code

[NiXXeD]

Currently:
-Regex based for matching urls
-Using excessively complex regex replace for embed urls
-Inconsistent iframe embed styles (should be reused)
-No unit tests

Ideally:
-Regex based for matching
-Url parsing for replacing see this
-More reusable embeds for iframes at least.
-Unit tests covering most/all scenarios to prevent regressions