Removed bool return value from LoadSettings()

The original intent was to indicate success or failure of loading
settings. However, it's not clear what success or failure means
because it is legitimate to not have a user- or site-settings file, so
indicating failure if one of these cannot be loaded is not really
accurate. Moreover, the return value wasn't used by the caller.

In addition, there was a bug in the previous implementation. If the
user settings weren't loaded, the site settings wouldn't be loaded
either. Now this method no longer returns any boolean value.

Change-Id: I039fc39aec3866e0d5b349fa43fc8f5c0d648d2a
Added PV_SETTINGS_DEBUG environment variable

When set, the application will print information about where settings
file are being looked for and whether loading them succeeded.

Change-Id: Ie98c568c417cef4bdbfb545ea5fe87bb3663453f
Try to load site settings files and use return value in search logic

Now instead of checking whether a settings file exists before
attempting to load it, we just try to load it and use the return code
from vtkSMSettings::AddCollectionFromString() to determine whether to
search other locations. This required fixing some of the behavior of
vtkSMSetting::AddCollectionFromFile() when the given file couldn't be
loaded.

Change-Id: Ic4f1caea33454453a4c7049c10642148a91f9cad
Added some more debugging macro statements

Change-Id: Ied84439e6743102e698814d1ef12c6d10c115ab5
If no user settings file is found, create a user settings collection

If this isn't done, then the site settings collection, if it exists,
will be treated incorrectly as the user settings collection, setting
changes will be saved there, and that collection will be written to
the user settings file.

Change-Id: I3581efc6ecc2bb2ae43f41854c7f8580776632e9
Merge topic '13575_PV_PLUGIN_DEBUG' into next

8d4ed01b If no user settings file is found, create a user settings collection
4ccb9ea3 Added some more debugging macro statements
ebd7c0e3 Try to load site settings files and use return value in search logic
c7f463ea Added PV_SETTINGS_DEBUG environment variable
ba08af44 Removed bool return value from LoadSettings()