Uncomment XML config line in Drawings and bug fix in Table.js

FIX:
- The 'toXML' function in Table.js was returning the wrong variable. It should return the 'doc' variable. Fixed in this commit.
- The uncommented line for an XML attribute in Drawings.js is required to generate an XLSX with images properly. Fixed in this commit.
Merge pull request #21 from riyadhalnur/bug-fix

Uncomment XML config line in Drawings and bug fix in Table.js