Bring redminenb to netbeans 8 compatibility

This is a big change set, I won't get into to many details and try to give a high level overview of the changes:

The changes acknowledge, that the inception of the stable api is a breaking change, that is worth breaking compatiblity. In consequence support for  netbeans version prior to 8 was removed. That move was completed by removing the remaining implementation dependcies, which break on each netbeans build and reducing the bundled modules to the bare minimum (I'd consider folding "Redmine Java API" into the main plugin module).

Query saving was implementing by introducing an xml representation of the datastructure - this is based on jaxb, which is integrated into the JDK and so future proof.

Basic testing was done and functionality that openly violated the contract not to do long running work on the EDT was moved to SwingWorkers where appropriate (I'm sure there are more places to fix, but at least it works right now).

GUI elements for issue journals and file handling were introduced and the GUI was reworked to be more efficient with regard to space use (for example when dealing with the markdown textile preview). Currently missing is a way to input/display time reports.

When file handling was added, the "Attach patch/file" functionality of the netbeans api was implemented. Pseudo implemented interfaces (issue status and issue scheduling) were removed for now, as they were implemented with a persistent cache in mind, which is not present in the current source state.

When going through the changes, please bear in mind, that the aim was to get this into a basic working shape, not perfection :-)