Previous version was only checking "isCompatibleWithInstalledVersion", but there were several other cases that had to be checked

Also removed the "sites" list from the init, since it seemed it was not being used, only using the specific site created from the external json

Now users can select "All", "Compatible" or "None"

Useful if the user first clicks "Select All" and now wants to "Select Compatible" only.

The UpdateSite class and its internal classes (e.g. Plugin) are a bit tricky to unit-test. Using some stubs to set the necessary context for the test to run

Had to remove the unit test checking "pluginUpdateNotCompatible. It needed "mock-maker-inline" config to mock/spy the Plugin class (which is final), but that mockito config caused conflicts with pre-existing tests.

Also switched the call in table.jelly to the overloaded version of isCompatible, since a "cache" var was available in the context (and was being already used by calls to the internal methods to show the warnings)

Trivial change to force re-execution of pipeline.

This method is currently only being used by the Jenkins UI, so we are not being exposing it to plugins nor exporting it. If in the future that need emerges, this can be changed