Support old PMD icons

[adangel]

There should be a configuration option to use the old icons instead of the shapes.

See also https://sourceforge.net/p/pmd/bugs/1151/

At the same time, the logic to change the shapes should be redone: Currently the icon files are replaced in the installation path of the plugin (which is impossible if this is a readonly location like in multiuser installs). The custom icons should be stored in the workspace state location.

When changing the icons, they should be used universally, also for the decorators. See also https://sourceforge.net/p/pmd/bugs/1212/.

[adangel]

The issues https://sourceforge.net/p/pmd/bugs/1151/ and https://sourceforge.net/p/pmd/bugs/1212/ are fixed with #98 / #85 .