Split helper class to separate source file

The use of nested static classes for SCIFIO components is a rather
special case; in general, is it best to avoid compounding several
classes into a single source file. In this case, the RAIS wrapper's
logic is independent of the BioFormatsFormat, so can live separately.
RandomAccessInputStreamWrapper: add @Overrides

These are overriding methods from a superclass,
so they should compile just fine even in Java 5.
RandomAccessInputStreamWrapper: remove javadoc

All of this javadoc is redundant with the superclass, and having it here
only serves to duplicate documentation. If the documentation were to
be improved upstream, those improvements would not be reflected in this
class due to the copy-pasting. Better to just remove them.

If a subclass really needs to make additions to the parent class's
javadoc, it can use the @inheritDoc annotation. But this implementation
was not adding anything new.
RandomAccessInputStreamWrapper: fix comments

These comments were all either obsolete or wrong due to copy-pasting
from other code, and/or APIs which evolved over time.
RandomAccessInputStreamWrapper: add javadoc links

It is nice to use the @link annotation to link to the relevant classes
being talked about. In this case, doing so also exposed an error in the
package of one of the mentioned classes.
RandomAccessInputStreamWrapper: remove javadoc

The javadoc in question did not really add any documentation,
and was not formatted according to SCIFIO convention, besides.
RandomAccessInputStreamWrapper: fix formatting