Added functionality to embed links into wiki

Enhancement Ticket #2308
According to a website link (http://sourceforge.net/p/bugs-bug-genie/wiki/markdown_syntax/#md_ex_video) TheBugGenie supports URL embedding, however I was unable to locate this functionality in the code or subsequent wiki's for TheBugGenie. Added in the functionality based on the Wiki from the link 

- Updated `core/classes/TBGTextParser.class.php`
	- Added case to search namespace for the embed keyword
	- format is similar to most namespaces, `[[embed:<url>(|width=X,height=Y,type=iframe|object)]]`, but it also supports `[[embed url=<url>(|width=X,height=Y,type=iframe|object)]]` which was the format specified in the wiki at the URL link above
		- `width` and `height` or optional, default values are set to 500 and 400 for width and height, respectfully
		- `type` is also optional, default value is iframe, object is the old way to embed youtube links
- Updated `core/lib/common.inc.php`
	- Added two functions to test youtube links
		- `tbg_youtube_link` to test to see if the url is a youtube link
		- `tbg_youtube_prepare_link` to update commonly used links to ensure they are form mated for proper embedding
- Updated `core/lib/ui.inc.php`
	- Added two new functions that support embedding
		- `iframe_tag` - returns iframe html
		- `object_tag` - returns object tag

Aslo added another test case - if the href is empty or set to 'embed' then this means an empty embed tag was entered `[[embed]]`, and further processing should be halted