Added optional button to clear the saved datatable state

Disabled by default, this button clears the localStorage or sessionStorage
before reloading the page to reset the datatable.
Ideally the page reload would be avoided and the table just redrawn, but
triggering the draw() function still seems to maintain table state even after
the localStorage.removeItem call
Moved placement of clear state button to the theme
Merge pull request #6 from loonytoons/clearState

Added optional button to clear the saved datatable state
Fixed bug that sorted table columns on filter select

The click event was bubbling up to the parent th element causing
an unintentional re-sort