feat: refactor: o.o.plugins package and plugin management subsystem

[miurahr]

Internal plugin management enhancement

Pull request type

Please mark github LABEL of the type of change your PR introduces:

• Feature enhancement -> [enhancement]

Which ticket is resolved?

What does this PR change?

• Introduce a package org.omegat.plugins and gather related classes; PluginUtils PluginInformation PluginInstaller PluginInstaller
• Move MainClassLoader to o.o.p.cl package
• Gather all the test classes related to plugin management into o.o.plugins
• Introduce new class o.o.p.PluginLifecycleManager class that support Plugins in a new way
• We use individual class loader instance for each plugin jar files. It allow plugins to use same but different version of library.

Other information

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