Remember & re-open last opened file

[Robert Leach]

When users are working on a file and quit, it would be nice if they were presented with an option to open the file that was last opened with a single click - like with a button next to the open button in the initial view, or also a select list of recently opened files with the last one opened pre-selected.

[Christopher Keil]

resolves #116; moved some status label code from TVController directly into WelcomeView. Colored status label red if no last file available

→ <<cset ee22804aec9e>>

[Christopher Keil]

fix for temporary ModelLoader bug introduced with last commit; resolves #116 by using an observer pattern to trigger readding listeners to the JMenuItems

→ <<cset 64586830f76a>>