SwingFileWidget: support 'pattern' style

[imagejan]

In addition to a style attribute like extensions:tif/tiff, we should support a way to define file name patterns, such as pattern:WildType*.tif (wildcard pattern) and/or pattern:^[A-Za-z0-9]+\.png (regex pattern).

Getting the style modifier will be simplified once scijava/scijava-common#405 is merged and released.

Open questions:

• Two different style attributes for wildcards and regexes? E.g. regex-pattern and wildcard-pattern, or regex and pattern, ...
• Additional flags to specify case (in)sensitivity? For regex patterns, we could use standard syntax like /[A-Z]/gmi or (?i)[A-Z]; I'm not sure about conventions for the wildcard case...

[imagejan]

In addition to regex patterns for filtering valid inputs, we should also consider how the usage of File[List]Widgets with file patterns in SCIFIO for actual inputs, see also scifio/scifio#431 and scifio/scifio#432 for related discussion.