ImgUtility/PlaneConvertService: remove public

Removed unnecessary public qualifier from methods in these interfaces.
MasterFilterHelper: prevent tail overwriting

Was always setting the tail at the end of initialization, which would
break the chain if any plugins were enabled by default.

Now, set the tail immediately, and allow any default enabled plugins to
chain naturally.
MasterFilterHelper: correct chain building order

When computing parents, was mistakenly setting the child as the parent.
The parent filter is now correctly the "older" and lower priority
filter.
Created FilterTest class

Adds unit tests for the Filter classes. Current tests focus on the
ReaderFilter class and ensure filters are initialized in the correct
order, and that the the defaultEnabled flag is functional.
Merge branch 'filter-tests'

Added unit tests for Filters, as well as fixes for issues exposed by these
tests.