On OS X, the default directory for files explicitly saved/loaded by the user is now ~/Documents/open-ephys.  Added CoreServices::getDefaultUserSaveDirectory(), which returns ~/Documents/open-ephys on OS X and the current working directory on other platforms.

On OS X, the default data directory is now ~/Documents/open-ephys, which is created if it doesn't exist

* Adjusted positions for play, record, master clock components;
* Adjusted positions for CPU and Disk meter components;
* Stylystic fixes.

* Implemented sliders' material lookAndFeel;
* Material lookAndFeel have been applied to sliders;
* Improved UI layout for panel.
* Adjusted positioning of elements during resizing.
* New icon for "Mute" button;