Isabelle Prover IDE support

This is an extension of the standard Isabelle2018 extension (and is not the official extension).

Isabelle2018 will not work and you need this version.

This extension supports:

1. the outline (and is rougly comparable to the sidekick of Isabelle/jEdit);
2. an indication of progress.

Point 1. is an a good shape (and will therefore be submitted for inclusion to the Isabelle-repository).

Point 2. turned out to be more complicated than expected.

If you intend to use this plugin, you should probably send me an email for instructions how to install it (in a few words: isabelle components -I, isabelle components -a, then the set-up is the same as the standard Isabelle2018 extension).