fix rtl mode #233

Hi, I just tried to fix issue #233 and some other problems I encounter during this bug fix.
I tried to find some contribution conventions on nicescroll but find nothing. so if there was any problem about my codes let me know :)

1. Fix #233 by setting horizontal scroll cursor absolute. to leave document flow and be independent of document direction (RTL-LTR)
2. completing rtlmode auto detect
3. un-commenting some of rtlmode codes to make it function correctly
4. fixing element.leftscroll property issues of FireFox.
5. adding a demo page for rtlmode

notes:
1. because of some bugs in hardware acceleration in RTL mode when using a wrapper. hardware acceleration should be disabled to have correct functionality.
2. in FireFox rtlmode horizontal scroll seats at the left side instead of right. at least it's working although in reverse of what it should behave.