Adding Named range and Table support

[akira215]

Still Work In Progress for table support, but basic functionalities are currently running (creating, browsing, ...). Corrected also some bugs with the Shared Strings items. To do so, the strategy of storing / accessing the shared string has been changed (stored in the document to avoid any copy, and access via the worksheet which are propagated through the objects). Its a huge pull request but I'm still working on table support to add capabilities:

• autofilter
• formatting
• more access fonctionalities

[akira215]

A new pull request as I am a little bit ahead with table functionality (formulas, styles, ..) I also corrected some bugs

[akira215]

adding functionality for table support. Missing autofilter implementation

[akira215]

Table support fully available