Grid object model

[rkaraivanov]

• Cell object implementation
• Row object implementation
• Grid - described below

Features not yet ported from the older version

• Drag and drop of columns
• Dialog editing

New features

• OnPush detection by default

• Inline editing with support for user templates

• Pagination with support for user templates

• Easier styling of rows, headers and cells

• Data Operations UI - PoC.
  @simeonoff is currently working on styling it.

• Code cleanup and documentation
  Do not merge this PR until we check this point

• Sufficient unit test coverage and scenarios
  Do not merge this PR until we check this point

This PR addresses issues #479 #480 #486 #489

[coveralls]

Coverage decreased (-5.8%) to 84.674% when pulling 1fee72e on rkaraivanov:grid-refactoring into 7c3c19e on IgniteUI:master.

[coveralls]

Coverage decreased (-5.8%) to 84.674% when pulling 751e5e4 on rkaraivanov:grid-refactoring into 7c3c19e on IgniteUI:master.

[coveralls]

Coverage decreased (-5.6%) to 84.875% when pulling 5064d1c on rkaraivanov:grid-refactoring into 7c3c19e on IgniteUI:master.

[coveralls]

Coverage decreased (-5.6%) to 84.855% when pulling 819f087 on rkaraivanov:grid-refactoring into ad7f2ea on IgniteUI:master.