Use pom-scijava as parent

This greatly simplifies the base Bio-Formats POM, allowing it to inherit
all of the SciJava configuration. This change makes the Bio-Formats POM
easier to understand, eases the maintenance burden of the Maven build,
and avoids many of Maven's common pitfalls.

Notes reiterated from ec8f5312e7336de4811d0c6bac3975b14602ec30:
> The pom-scijava parent POM provides lots of technical benefits,
> including many configuration convenience blocks, as well as
> workarounds for various bugs, etc. By extending pom-scijava,
> Bio-Formats automatically inherits this helpful configuration, so
> that it can avoid painfully encountering all the same issues which
> have already been solved in other SciJava projects.
>
> On a social level, extending pom-scijava also signifies that the
> Bio-Formats project is part of the SciJava software stack.
>
> Since the org.scijava:pom-scijava artifacts are now available in
> Maven Central, there is no more issue with this dependency resulting
> in any reference to the maven.imagej.net Maven repository.

Further, since Maven is a "convention over configuration" system, it is
always possible to override configuration inherited from pom-scijava, in
cases where Bio-Formats needs to do things differently. And since the
pom-scijava parent reference is a release version, there is no
possibility of upstream changes to the parent POM affecting Bio-Formats
until Bio-Formats explicitly bumps the version upon which it depends.

This reverts commit fcbb16ac8d7580fe85987862a3bf76cfab57818d.