Return image url basing on path('public')

Replace pattern was taking hardcoded '/public' to generate image url in editor. It was not consistent with user setting. Now it strips proper public path.
Merge pull request #58 from exlee/patch-1

Return image url basing on path('public')
Change to the Image field
It now supports two ways of specifying upload path
either by:
'location' => 'path/relative/to/public/'
or by:
'location_upload_path' and 'location_upload_url'
(first one specifies absolute path for upload, and second
the return url to which attach filename).

Also, 'location' supports 3 types of locations:
path('public').'some/path'
'public/some/path' and
'some/path'
Merge remote-tracking branch 'upstream/master'

Conflicts:
	Libraries/Fields/Image.php