BugFix: Can add new line at the bottom of table without exception after table was sorted
Bugfix for wrong column sorting: It can be reproduced by following steps:
1.) ensure there are many columns so that horizontal scrollbar appears
2.) scroll to the right
3.) sort a column via sort link in column header (for example the first visible column)
The table sorts the very first column, not the first visible column.
Bugfix #793. Fixes many issues with CRUD operations on sorted table.
Bugfix #542. Added fix for sorting table with column offset by tansin (github.com/tansin).

Merge commit '5c50f554834909f540bb1b6cb0e89dcb4a96b264' into feature/bugfix-#542
Merge branch 'feature/bugfix-#542' into feature/bugfix-#793
Bugfix #720. Added proper sorting of column with type "date". As for now, sorting works fine with date strings that can be parsed by Date.parse() function.
Bugfix #746. Fixed sorting tables with more than one row header.
Replaced saving data in cookies with localStorage.
Merge branch 'feature/bugfix-columnSorting' into feature/saving-table-state

Conflicts:
	src/plugins/columnSorting.js
Tests for modified columnSorting plugin