Scroll DataTables-enhanced tables horizontally by default.

git-svn-id: https://plugins.svn.wordpress.org/inline-google-spreadsheet-viewer/trunk@965312 b8457f37-d9ea-0310-8a92-e5e31aec5664
Add `FixedColumns` extension, support setting params in `class` values.

git-svn-id: https://plugins.svn.wordpress.org/inline-google-spreadsheet-viewer/trunk@965317 b8457f37-d9ea-0310-8a92-e5e31aec5664
Update documentation, version bump to 0.4.7.

git-svn-id: https://plugins.svn.wordpress.org/inline-google-spreadsheet-viewer/trunk@965318 b8457f37-d9ea-0310-8a92-e5e31aec5664