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.

this should reduce the impact of the remaining 1px plot issue until we
track it down

non plugin specific class defs should not go into the plugin specific namespace

this range makes saturation bounds visible, useful for testing if
behavior rigs work etc.

the correct value seems to be 6389 for this gain setting etc. 2do:
double check that

though there is still a small display issue if the end of the display
buffer is hit because now only 1-2samples are associated with the pixel
and this causes the min/max and histogram displays to look odd.
shouldn’t be a big issue in real applications but worth fixing when we
inevitably refactor this whole plugin.

* LinearButtonGroupManager class now have the same functionality as
  ButtonGroupManager class had before.
* ButtonGroupManager now is the base class for all other button group
  managers.
* Appropriate fixes in the CAR plugin.