Refactoring and documenting the markup tags and attributes

Refactoring and documenting the markup tags and attributes

Moved all tags and attributes to separate file.
Added doxygen description for each tag and attribute.

To check doxygen documentation:
   1) Build dali-toolkit
   2)Generate the internal documentation for DALi Toolkit
     https://github.com/dalihub/dali-toolkit/tree/master/docs/generated-internal
   3) Goto: Files > File List > dali-toolkit > internal > text > markup-tags-and-attributes.h

Change-Id: I42693d0c1ce1169614ccad9391ef4f60a04b3f66