Added helper for document pre-order traversal.

Change-Id: I134db5c93f99edde7bbcabbb7fde81de839e7d2b
Data model implementation for tables.

Introducing dm.TableMatrix, a companion for dm.TableNode that provides a
non-sparse representation of tables with spanning cells.

Change-Id: Ib4afcbaf157fb64666f52c9650f3260bb42f2a3c
ContentEditable implementation for tables.

ve.ce.TableNode provides some visual sugar via overlay to display the table
selection.

Change-Id: I3d5509315e6f09138409bcaf4e39914874082353
Actions for manipulating tables.

ve.ui.TableAction contains actions as well as a generic table manipulation API.
The API does only depend on DM and could be moved to DM world someday.

Change-Id: I261a4169108f5ec64926b9d7af9e352586ab800a
Icons and tools for table manipulations.

Change-Id: Ic76f329fcb6cd5c8c7a8a1a8c16d1e9ebd74fe51
I18n for table tools.

Change-Id: Ie4557f1a8bffd976a456d88d8c1433b0c4dec546
Add table example and include necessary source files in demo.

Change-Id: Ia8d80a5388d115f987459ceb3ba757ad1cccef1f
Custom sub-toolbar for table tools.

Change-Id: I243570a76235b569b93b47f238df2c25bb3e7a12
Provisional fix to prevent structural changes to a table via delete+merge.

Change-Id: I5229e55e0e83b29f1329f4c378caff77f2db0581