Support for 4.X Kernels

[TheNetStriker]

This library doesn't work with 4.X kernels. I figured out that a small adjustment in the BBBSysFs.java fixes the problem. With the 4.X kenels the SYSFS_DEVICES_PATH must be set to "/sys/devices/platform".

I've also added those two lines at the beginning of the isSlotLoaded(int slotIndex) method to prevent an error if the HDMI cape isn't loaded:
if (slotIndex == -1)
return false;

Could you please implement this and set the SYSFS_DEVICES_PATH variable based on the kernel version?

[TheNetStriker]

I've created a pull request for this: #25
I also found an error in PCA9685Pwm.