sticky header can respect height of a top navbar

this is no option at the moment and is only accessable modifying the
code direct
scrollbars can handle top and bottom navbars

at the moment this behaviour can not be controlled by any options. code
ahs to be modified for this.
added doc folder with index.html playground
sticky header does not longer mark the original table header with table-sticky-header-row-original class
sticky headers is not longer changeing the original table header

sticky headers are now a deep copy clone and appended to the table
header
cleaned navbar handling on sticky headers and scrollbars
corrected typo in table-scollbar and renamed it to table-scrollbar
added 2nd header row in table on example page
added options to plugin

navbar top and bottom height can be set via options now
refactored plugin so that style is more like other bootstrap plugins and slightly changed api druoing refactoring.
moved sortable feature init to end so that sticky headers gets first initalized and the icons are displayed.
icon handling on sorting is now more robust the clicked column is referenced by this
first shot of a working destroy functionality for sticky headers and the scrollbar