WidgetModel: fix getMin/Max javadoc

It was slightly incorrect before; the reality is that it only gives back
null if the type is unbounded (e.g., BigInteger). For any bounded type
(e.g., double), you will get back a minimum/maximum bound corresponding
to the absolute minimum/maximum of that type, even if no min/max
attribute was specified in the @Parameter annotation.
WidgetModel: factor out common boilerplate code

It is more concise to put the common numerical type conversion logic
into a private toNumber method.
ModuleItem: add getSoftMinimum/Maximum methods

This change also adds corresponding setSoftMinimum/Maximum methods to
the MutableModuleItem interface.
WidgetModel: add getSoftMin/Max accessor methods

These correspond to the new ModuleItem#getSoftMinimum/Maximum methods.
SwingNumberWidget: respect soft minimum & maximum

This requires a bugfix in scijava-common 2.0.2 to work as expected:
https://github.com/scijava/scijava-common/commit/12a35ee1b742a84b870a03a36717a3d9c8bd5876
BrightnessContrast: set soft minimum & maximum

This makes the behavior more consistent with ImageJ1: the Minimum and
Maximum fields now have sliders which are bounded by the *data* minimum
and maximum. You can still use the spinners to explicitly set the
minimum and maximum values outside the range of the sliders (by either
explicitly typing a number or by using the spinner arrow buttons), but
if you use the sliders directly you will be bounded by the data min/max.
Merge branch 'soft-bounds'

This branch adds support for a separate "soft" min and max bounds on
numeric parameter, distinct from the existing "hard" min and max values.

These soft bounds are a recommendation for certain intrinsically bounded
UI components such as sliders and scroll bars. The Swing UI has been
updated to respect soft bounds when using the NumberWidget.SLIDER_STYLE
or NumberWidget.SCROLL_BAR_STYLE parameters.

This branch also updates the Brightness/Contrast dialog to use scroll
bars with soft bounds for its Minimum and Maximum parameters, which
addresses the long-standing ticket #1803:

http://trac.imagej.net/ticket/1803
Remove obsolete datestamp

Eclipse 4.3 removes them automatically.
Change base POM name to pom-imagej

The name "pom-imagej" is still unique (does not clash with any other
project or any directory name), while better conforming to other
Maven-based multimodule projects in the SciJava ecosystem such as
ImgLib2 and SCIFIO.

The name "pom-imagej" is also a better hint for what to call the tag
when releasing a new version of ImageJ ("imagej-2.0.0" is a better tag
name than "ij-base-2.0.0").