GEOT-7289 Java 9 dependency conflict fixes

[liturner]

Merged jt-scale with jt-scale2 (deleting jtscale2) and bumped the guava version in order to improve Java9 Module compatibility.

Relates to https://osgeo-org.atlassian.net/browse/GEOT-7289

This approach has the least impact to the consumers of jai-ext as there are no class or package name changes (jt-scale2 classes each already have unique names and reside in the same package). Other solutions would require downstream projects to refactor their code (e.g. if we were to rename the package).

Downstream Impacts

• Users of jt-scale will now have an additional dependency on BigInt. Note that this package does not contain license information in its POM which will trigger warnings in tools like the maven license-maven-plugin. A pull request has been openened in the source repo to resolve this moving forward.
• Users of jt-scale2 will have to switch to the jt-scale maven dependency.

First PR

This is my first PR on this Repo. Maven using Java 8 is successfully "verify"ing on my machine, but I am unsure of how I can further verify the intended functionality. If I have missed any documentation anywhere please let me know!